This patch allows building the project without Qt WebEngine, by
disabling (for the time being) the features that depend on it:
the emoji picker, link previews, and media file previews in the
chatview.

Co-authored-by: Andreas Traczyk <andreas.traczyk@savoirfairelinux.com>
Co-authored-by: Amin Bandali <amin.bandali@savoirfairelinux.com>
Change-Id: I74751b0cc6f22c61a6fd7281ca3207e0fdbb2212