Change thickbox to a better plugin

While analysing the code of admin side I realised we’re still using thickbox, although it has been deprecated long time ago.
I think that we should start using fancybox or some other well supported/developed plugin for our popup content.
A lot of other software (like e.g. Atlassian jira) already use fancybox and it’s working very nice.
This might of course need much effort to change/maintain/fix but that would be a really nice improvement.