Moved essential depndency-less plugins into Magnum repository.

MagnumFont, MagnumFontConverter, TgaImporter, TgaImageConverter and
WavAudioImporter plugins has been moved along with whole history into
Magnum.
Updated FindMagnum.cmake from Magnum repository.
Fixed the build after plugin removal.
FindMagnumPlugins.cmake: ability to find also dynamic plugins.

Thus it is now possible to use them as dependency.
FreeTypeFont: skip the test case instead of failing whole test.

Makes automated testing huge PITA.
JpegImporter: initialize ColorFormat to some value.

Fixes compiler warning.
Use ninja in development PKGBUILD.
Remove inexistent plugins from MinGW PKGBUILD.