package: fix PKGBUILD error.
package: use Ninja in all development PKGBUILDs.

Also remove obsolete options (these plugins are now in Magnum itself).
Adapted to Magnum changes.
Updated FindCorrade.cmake from Corrade repository.
Merge branch 'master' into compatibility

Conflicts:
	modules/FindCorrade.cmake
modules: updated FindCorrade.cmake from Corrade compatibility branch.