VcsBase: URL and email support in log editors

URL and email addresses are recognized in log and annotate
editors so the user can interact with as it is usually done
with VCS change identifiers.
The design of "text cursor handlers" opens the path for
further support of other contents like bug id of the
form "QTCREATORBUG-XXXX".

Change-Id: I88f553cf8ac90678ace52144ba0b43604279a234
Reviewed-by: Tobias Hunger <tobias.hunger@nokia.com>