A little polish

• Fix race on IE with scrollport initialization.
• Fix ctrl-shift-esc handling on OS X.
• Always use the text cursor in the terminal.
• Fix 8-bit help text in options page.
• Allow zoom warning to be dismissed.

hterm 1.56, freshen up the options page

• Update to hterm 1.56.
• Use hterm's new pref category and data type data to improve the options
  page.

pref shuffle, keybindings, utf-8, and Mouse reporting

• Fix mouse reporting. Previously users had to click, then move the mouse
  before mouse reporting would start.
• Deal with surrogate pairs more properly.
• Add customizable keybindings.
• hterm_preference_manager.js: Group prefs into categories, declare input types
  rather than guess based on default value, improve layout.