BUGFIX: Don't include deleted topics in activity. Deleted posts are OK.
FEATURE: better UX when backing-up the site

Users won't be prompted whenever the site goes into read-only mode.
Instead, a banner will be shown at the top of every pages.

Also, the browser won't automatically reload whenever read-only mode is
disabled. This really was bad UX.
OPTIM: change Top Topic's score computation algorithm

New algorithm will not wipe the entire table anymore and will only remove
invisible topics and add new visible topics.
Version bump to v0.9.8.8
Upgrade ember-cloaking to not trigger scroll events when the back button
is hit.
Make the back button less awkward when leaving a topic.
BUGFIX: Fix issues if the DOM element is destroyed while the interval
is ongoing (in particular this was weird for Firefox)
Merge remote-tracking branch 'upstream/master'