Update filters on resize and screen events.
Activate link filters on ctrl+click.
Add UrlFilter.
Derive Filter from QObject.
Emit UrlFilter::activated() instead of QDesktopServices::openUrl().
Added QTermWidget::urlActivated(QUrl) signal.

Relays the corresponding UrlFilter's signal.
Merge pull request #20 from 0xd34df00d/autolinks

Links highlighting and handling