Fix select branch list scrolling

[WizardOhio24]

Closes #368

The scrolling in branch list is now the same as the commit-list and the file-list, in that it scrolls only at the top or the bottom and can change speed.

[extrawurst]

this crashes on small terminals:

panic: PanicInfo { payload: Any, message: Some(attempt to subtract with overflow), location: Location { file: "src/components/select_branch.rs", line: 62, col: 35 } }
trace:
   0: backtrace::backtrace::libunwind::trace
             at /Users/stephan/.cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.53/src/backtrace/libunwind.rs:100:5
      backtrace::backtrace::trace_unsynchronized
             at /Users/stephan/.cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.53/src/backtrace/mod.rs:66:5
   1: backtrace::backtrace::trace
             at /Users/stephan/.cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.53/src/backtrace/mod.rs:53:14
   2: backtrace::capture::Backtrace::create
             at /Users/stephan/.cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.53/src/capture.rs:176:9
   3: backtrace::capture::Backtrace::new
             at /Users/stephan/.cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.53/src/capture.rs:140:22
   4: gitui::set_panic_handlers::{{closure}}
             at src/main.rs:300:25
   5: std::panicking::rust_panic_with_hook
             at /rustc/18bf6b4f01a6feaf7259ba7cdae58031af1b7b39/library/std/src/panicking.rs:573:17
   6: std::panicking::begin_panic_handler::{{closure}}
             at /rustc/18bf6b4f01a6feaf7259ba7cdae58031af1b7b39/library/std/src/panicking.rs:476:9
   7: std::sys_common::backtrace::__rust_end_short_backtrace
             at /rustc/18bf6b4f01a6feaf7259ba7cdae58031af1b7b39/library/std/src/sys_common/backtrace.rs:153:18
   8: rust_begin_unwind
             at /rustc/18bf6b4f01a6feaf7259ba7cdae58031af1b7b39/library/std/src/panicking.rs:475:5
   9: core::panicking::panic_fmt
             at /rustc/18bf6b4f01a6feaf7259ba7cdae58031af1b7b39/library/core/src/panicking.rs:85:14
  10: core::panicking::panic
             at /rustc/18bf6b4f01a6feaf7259ba7cdae58031af1b7b39/library/core/src/panicking.rs:50:5
  11: <gitui::components::select_branch::SelectBranchComponent as gitui::components::DrawableComponent>::draw
             at src/components/select_branch.rs:62:35
  12: gitui::app::App::draw_popups
             at src/app.rs:626:9
  13: gitui::app::App::draw
             at src/app.rs:205:9
  14: gitui::draw::{{closure}}
             at src/main.rs:184:25
  15: tui::terminal::Terminal<B>::draw
             at /Users/stephan/.cargo/registry/src/github.com-1ecc6299db9ec823/tui-0.12.0/src/terminal.rs:259:9
  16: gitui::draw
             at src/main.rs:183:5
  17: gitui::main
             at src/main.rs:149:13
  18: core::ops::function::FnOnce::call_once
             at /Users/stephan/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/core/src/ops/function.rs:227:5
  19: std::sys_common::backtrace::__rust_begin_short_backtrace
             at /Users/stephan/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/std/src/sys_common/backtrace.rs:137:18
  20: std::rt::lang_start::{{closure}}
             at /Users/stephan/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/std/src/rt.rs:66:18
  21: core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &F>::call_once
             at /rustc/18bf6b4f01a6feaf7259ba7cdae58031af1b7b39/library/core/src/ops/function.rs:259:13
      std::panicking::try::do_call
             at /rustc/18bf6b4f01a6feaf7259ba7cdae58031af1b7b39/library/std/src/panicking.rs:373:40
      std::panicking::try
             at /rustc/18bf6b4f01a6feaf7259ba7cdae58031af1b7b39/library/std/src/panicking.rs:337:19
      std::panic::catch_unwind
             at /rustc/18bf6b4f01a6feaf7259ba7cdae58031af1b7b39/library/std/src/panic.rs:379:14
      std::rt::lang_start_internal
             at /rustc/18bf6b4f01a6feaf7259ba7cdae58031af1b7b39/library/std/src/rt.rs:51:25
  22: std::rt::lang_start
             at /Users/stephan/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/std/src/rt.rs:65:5
  23: _main

[WizardOhio24]

Fixed

[extrawurst]

@WizardOhio24 thank you so much for for continuing support!❤️