shell: Display generic project managers again
Summary:
This fixes a regression in 3a74e103e03a which prevents empty filter lines
in the file dialog, but also removes plugins with empty filters from
the list of project managers.
This commit adds a second list for generic project managers to avoid
storing these in the project filters list.
Test Plan: Launch KDevelop, open the Import / Open Project dialog, select an empty folder, and click next. The Generic Project Manager should be shown in the dropbox.
Reviewers: KDevelop, mwolff, kossebau
Reviewed By: KDevelop, mwolff, kossebau
Subscribers: kfunk, brauch, mwolff, kossebau, kdevelop-devel
Differential Revision: https://phabricator.kde.org/D12279