Desktop notifications

When quoted or syncwatch is about to start
Tweak desktop notifications

Use bigger favicon and the Visibility API
Allow syncwatch without hours.
Accurate file sizes
Add missing `var`
Move some globals to init.js
Provide CurThread
Remember whether focus was manual or not
Don't jump to thread bottom on reconnect

Rather, we auto-focus on the last post. Idea by @bakape.

Closes #97.
Don't auto-focus until dropped for 10 seconds
ffmpeg thumbnail filter

Use `-vf thumbnail` for more meaningful WebM thumbnails.
Prevents false positives on perceptual first frame hashes
Fix WebM error handling
Write [See all] link upon seeing first reply
[See all] remembers your position
Improve gar and mawaru theme responsiveness

* Significantly increases responsoveness with the gar and mawaru theme in large threads
* Avoids Firefox bug https://bugzilla.mozilla.org/show_bug.cgi?id=671302
Show [Top] link on non-iOS mobile devices

Addresses #75.
Revert "Sync last post on connection drop"

This reverts commit f417abd73fb12d964c96675fdccd3664da1f4350.
Superseeded upstream by 5509f858575c4d93d57d1fce678206cd1098f4b3..d03c5e3a8e6ef4a44b8dbcd5c8b91b1e069f3594
Merge remote-tracking branch 'samu/master'
Mobile detection: check for mozOrientation too

Addresses #75.
Only roll dice after confirming post reservation