Enforce plaintext for status message

## The fixed bug:
Previously, if you set a status message Qt assumed to be HTML like `a<b>c`, Psi actually send it as `ac`. 

## New features:
Since a ChatEdit is used, the Status Dialog now supports spell checking.

## To be considered:
I've rebased 3 old commits on top of the current master branch, noticing that in the meantime (1a00d690f1695a4753185f5941f487bec109e7e8, to be exactly) the original ChatVIew was replaced by a PsiTextView. Since this was done in a webkit related commit ("Added webkit support from Psi+"), I'm not sure what the relevance of this change was.