inspect file tree at revision

[extrawurst]

a fullscreen popup (just like the file blame) that allows inspecting the entire file tree of the repo in a particular revision. this can be opened from the revlog.

features:

• open files tree from log / commit detail
• reusable and more efficient file-tree view (with recursive collapse/expand)
• new reusable tree nav common bar entry with proper help text
• go into blame of a selected file
• show content of selected file

post MVP:

• use syntax highlighter (integrate syntax highlighter in file-tree-view #725)
• go into file history of that file (requires View log/history of a file #381)

[extrawurst]

MVP done