Fixed the heads up layout of conversations

Previously the expand button layout was always at 80dp which
made the collapsed size increase. we now measure it at
match_parent instead and just internally use another layout
to position it properly.

Fixes: 153204251
Test: add heads up notification, observe normal padding
Change-Id: I76df6529c1a24808bce54ed0d04230cddf7a0c8c