Enforce plaintext for auto-away status message

Don't let Qt guess if the auto-away status message contains HTML.
Merge pull request #159 from FlorianFieber/fix-plain-status

Enforce plaintext for auto-away status message
Fix copy&pasting rich text into status message options
Switch status message options from QTextEdit to ChatEdit

Thus enabling spell-checking
Merge pull request #160 from FlorianFieber/fix-plain-status

Fix copy&pasting rich text into status message options