Revert "add mentions to TinyMCE"

This reverts commit 7b5d310b5891e31eccdb212586440bd4039071f9.
Revert "Revert "add mentions to TinyMCE""

yeah yeah, I know this isn't awesome, but I had pushed it to staging and wanted to see it work.

This reverts commit 2108f3f502630a9cc5c37789650126329943cc04.