Add qtc-sourcetrail to Qt plugin repo

[vincent-hui]

qtc-sourcetrail can get mechanical adapted to API changes of qtc if you submit qtc-sourcetrail to the Qt Creator source on codereview.qt-project.org and it is accepted there.

[vincent-hui]

Thank you very much for open-sourcing Sourcetrail. Do you have a plan to submit qtc-sourcetrail to the Qt Creator source on codereview.qt-project.org? That can save maintenance time and help promoting Sourcetrail.

[mlangkabel]

Yes, now that we are open-source I think that it makes much more sense to submit the plugin to Qt Creator, since everybody can use it now.