ui: Remove label test of hidden GtkLabels
TweetListEntry: Set correct link handler of rt_label

... woops.

Conflicts:
	ui/tweet-list-entry.ui
ImageLabel: Don't crash if no icon is set
Timelines: Scroll up when activated but already active

Also, don't use switch_page when switching to the first timeline
on startup.
Profile-/TweetInfoPage: Switch to TweetInfoPage when tweet is activated
HomeTimeline: Don't force_wait on scroll_top_next

This caused the user to be unable to scroll down whenever he received
mutliple tweets when not being at the HomeTimeline when they arrived.
Related to #49.
TweetInfoPage: Fix scroll_event callback

... so scrolling down is possible again. m(
ScrollWidget: Don't add more than 1 callback for scroll_up

This should hopefully finally solve the wrong scrolling.

Conflicts:
	src/HomeTimeline.vala
	src/MentionsTimeline.vala