[Merge] lp:~phablet-team/messaging-app/compose_bar into lp:messaging-app

[Arthur Mello]

Review: Approve

Talking with Gustavo, it was decided that minor issues mentioned at comments will be addressed on further MRs. Besides that code lgtm
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https://code.launchpad.net/~phablet-team/messaging-app/compose_bar/+merge/280488
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