Make buttons unselectable

This improves copying and pasting quite a lot
Support narrowing buffer selection with Alt+0-9 after using Alt+g or when onlyUnread is enabled, and show numeric overlays for Alt+0-9 keys on the buffers
Quick keys disappear only after releasing alt key

Other changes:
- 0.2s delay so they don't appear when pressing Alt+A etc
- don't appear when other modifier keys are pressed
Merge pull request #482 from glowing-bear/make-buttons-unselectable

Make buttons unselectable
some scrolling updates
Fix bufferlist spacing on mobile

The current version is much too tight to hit, and for some reason I only
fixed it in the cordova branch. This should go into master, though.
Restore space at the bottom of buffer lines
Merge pull request #486 from glowing-bear/fix-buffer-bottom

Restore space at the bottom of buffer lines
fix $apply exception on showSidebar
make pageup key trigger fetch more lines
index: be extra careful to escape space in order to avoid uncollapsed space with white-space:pre
Merge pull request #489 from ailin-nemui/sidebar-apply-ex

fix $apply exception on showSidebar
Merge pull request #490 from ailin-nemui/pgup-fetch-lines

make pageup key trigger fetch more lines
Merge pull request #491 from ailin-nemui/escape-whitespace

index: be extra careful to escape space in order to avoid uncollapsed space with white-space:pre
Fix inline colour filter by applying to text nodes only

this requires traversing the line's DOM and manipulating things there
Merge pull request #492 from glowing-bear/fix-filters

Fix inline colour filter by applying to text nodes only
Merge pull request #485 from glowing-bear/fix-bufferlist-spacing

Fix bufferlist spacing on mobile
Merge pull request #483 from glowing-bear/key-overlays

Show quick access keys on Alt keypress
Merge pull request #484 from ailin-nemui/scrolling-poll2

[Please test] some scrolling updates via polling
[light theme] add style for quick keys