Dirty little parser to enable clickable URLs

Still messy, hyperlink button needs proper positioning figured out, and
could potentially add a lot more smart parsing: recognizing pictures,
videos, etc.
Cleanup after the previous changes

Moved hyperlink margin/etc. to a XAML style, added reminders for future
fixes, some minor reorganization and safety checks
Merge pull request #3 from zsgalusz/origin

Clickable URLs in messages