Migrate tcell to 2.0.0
* tview.TreeView#SetSelectedStyle removed
* tview.Primitives don't allow directly setting attributes for now (might change again with tview 2.+)
There were scenarios where the user tree would be shown in a bad
situation, or be shown / not shown incorrectly. It would also be shown
on startup, even though no guild or groupDM was loaded.
* mutex instances have been removed from components, instead the
components are mutexes themselves now
* vtxxx checks have been replaced with tview calls
* duplicated code has been removed
Marcel Schramm