search-page: Use activate-on-single-click
TweetListBox: Only toggle modes for TweetListBoxes
BadgeRadioToolButton: Don't take focus on click
UserStream: Stop the network timeout when stopping the stream
UserStream: Start the heartbeat timeout in start()

Otherwise, the stream could return NULL and we would never call
start_heartbeat_timeout in that case, causing the stream to never be
restarted.
UserStream: Don't remove 0 source
settings-dialog: Use MB instead of Megabytes

See #289
ImageCropDialog: Properly localize plurals

See #289
DMThreadEntry: Properly localize plurals

See #289
DMThreadEntry: Properly localize plurals

See #289
HomeTimeline: Properly localize plurals

See #289
pot update
Merge branch 'master' into no-hover-buttons
TweetListBox: Add spinner_size property
tweet-info-page: Use smaller placeholder spinner