Allow multiple lines in input field

Dino.im handles it in a way I like personally.

added T: feature label

changed milestone to %GTK Next

What makes it a lot easier is to implement the emoji button on our own with a separate button beside the input field. Then, we can easily use TextView which is GTK's multi-line input method.

added Good first issue Usability labels

added S: diagnosed label

mentioned in commit 9adee7c9

mentioned in commit 5868cc0b

mentioned in merge request !92 (merged)

assigned to @nicoalt

closed with merge request !92 (merged)

changed milestone to %GTK 0.1.0-beta3