Rewrite the Makefiles to adapt the subdir-objects philosophy

For VST:
- Make a vst subdir with its own Makefile.am
- This should copy the vst sources from VST_BASEDIR and compile them locally into a staitc nodist lib.
Makefile.am.drumgizmo and Makefile.am.plugingui should be removed. All files should be compiled in as many variations as needed into .a files which can then be references from the other Makefiles