refactor startIconBlinkingMaybe()
support urgency hint
do chat icon blinking ourselves

gtk_status_icon_set_blinking() deprecated deprecated since version 2.22,
removed in GTK+ 3
cleaning
implement experimental cross-fading for blinking chat icon
handle blinking on new messages for twitter accounts

No 'new-directed-incoming-message' event is issued on new messages for twitter
accounts, which seem to be considered chatrooms (instead of private
conversations).
Merge branch 'twitter-blink' into icon-blink

Conflicts:
	src/modules/FiretrayChat.jsm
* use a pool of conversations for handling attention calling
* ignore messages from self (can be sent from other application)
bump Zotero version to 4.*