Register kdevelop as handler for repo urls, add --fetch argument

Summary:
Allows to speed-up the import of new projects, just clicking a repo url
would start a kdevelop instance right into the import dialog, with data
prefilled.

Using --ps argument with the handlers allows to keep control with which
session a project should be fetched.

Test Plan:
Calling kdevelop --fetch git://anongit.kde.org/kdevelop.git starts last
kdevelop session right into fetch dialog.
Invoking a handler onto a git://anongit.kde.org/kdevelop.git starts
kdevelop, asks for session and then proceeds into fetch dialog.
DnD of repo urls onto the mainwindow works as before

Reviewers: KDevelop, apol, kfunk

Reviewed By: KDevelop, apol, kfunk

Subscribers: kfunk, apol, kdevelop-devel

Differential Revision: https://phabricator.kde.org/D8830