Add PerforceImportMetadataWidget.

Not all functionality is implemented in this commit. Subsequent commit(s) will contain the rest of the functionality.

The widget makes some very basic tests to

a) See if the perforce client executable is a valid one
b) Test if the specified repository server url is valid
c) Test if the repository contains client workspaces

and reports to the user if any of the tests fail

It currently does NOT save any of you configuration when you import/create a new project. Therefore, anything entered in the widget is currently not usable to KDevelop.

Reviewers: KDevelop, apol

Reviewed By: KDevelop, apol

Subscribers: kdevelop-devel

Tags: KDevelop

Differential Revision: https://phabricator.kde.org/D14382