Fix issues releated to mention menu.
Fix issues releated to mention menu.

1. Fix cursor position after a user is selected, which would jump to the first character after a user. This is resolved due to the change of implementation. Now use insertToEditArea providede by angular scope instead.
2. Fix message sent right after a user is selected, which would cause inserted user name not digested by angular and would not be included into the message text.

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