Alter message on auto-update

Avoid ambiguously implying that Linux users should be running Zotero as
root, and tell them to fix the permissions on the Zotero executable instead.

See https://forums.zotero.org/discussion/31020/
Use Ctrl-Shift for all shortcuts on Windows/Linux instead of Ctrl-Alt

https://forums.zotero.org/discussion/25927/#Item_5
Fix warning in Nightly about yield without a value
Blacklist Firefox HealthReport errors
Add Firefox-wide shortcut (Ctrl/Cmd-Shift-S) for "Save to Zotero"

Also: Don't show Firefox-specific shortcut keys in Standalone prefs
Optimize local file modification checks during file syncs

- On manual sync or the first auto-sync of a session, check all files
- During other auto-syncs, check only files previously modified or
  opened externally via Zotero (including Show File) within the last 3
  hours
- Every 3 hours, do a full check of all files even if it's an auto-sync
- Spin event loop during synchronous file checks to avoid hanging the UI
- Zotero.Sync.Runner.sync() now takes an options object (e.g.,
  options.background)

Todo:

- Provide feedback on last full check in sync icon tooltip?
- Auto-sync on app focus, if this speeds up syncs enough?
File sync optimizations
Closes #77, Create linked files with drag and drop

The cursor effect doesn't work reliably anywhere other than on Linux,
but external files can now be linked instead of stored with
Cmd-Option-drag on OS X and Ctrl-Shift-drag on Win/Linux.
Fix error exporting linked HTML file

https://forums.zotero.org/discussion/29392/#Item_14
Update auto-update pref text to include styles
Use async I/O for attachment (blue dot) column file check in Fx23+
Fix note resetting in external note window during file syncing

https://forums.zotero.org/discussion/29008
Update locales from Transifex
Update submodules, repotime, and versions
Focus Close button by default in About pane
Capitalize Q library in About pane
Disable some debug logging for file syncing
Include libraryID in file sync debug message
Closes #311, Update RIS/Refer pref to mention BibTeX too
Use async DB for autocomplete

This was probably hanging previously because I was passing a JS function for
onProgress, which apparently isn't allowed.