[server] Update replies count
[server] Update replies count

Test Plan:
Send text message in sidebar and check replies count - it should be increased.
Change sidebar color - replies count should be the same.
Send text message in parent thread - replies count should be the same.

Reviewers: ashoat

Reviewed By: ashoat

Subscribers: KatPo, zrebcu411, Adrian, atul, subnub, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D683

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