Add "Mention user" button to user card

Closes #639 (closed)

added 12 commits

• adb67ca5...dcef8436 - 5 commits from branch pleroma:develop
• 5ff899b4 - add mention button
• 90981dcc - remove needless condition
• f4bbf1d4 - add new module and modal to post new status
• a9f33272 - refactor MobilePostStatusModal using new PostStatusModal
• 0c8038d4 - recover autofocusing behavior
• d6a941a1 - rename component
• c8a18f38 - wire up props with PostStatusModal

Compare with previous version

mentioned in commit ccba92a2

merged