issue #799 merger message views (#876)

On Room Actions, we have Files, Mentions, Starred and Pinned.
They have similar APIs and logic.
All of those could be merged into one generic view (MessagesView).
Maybe even Search could be in this merge.

Note: They're similar, but have own rules (unstar, unpin, etc).

This change may reduce 1MB to our release bundle size, since we're going to remove a lot of boilerplate.