Updated the Makefiles and updated testplugin to new plugin interface.

user: Roeland Merks <roeland.merks@cwi.nl>
branch 'default'
added src/Makefile
added src/build_models/Makefile
changed src/VirtualLeaf.pro
changed src/build_models/leafplugin.cpp
changed src/build_models/leafplugin.h
changed src/build_models/testplugin.cpp
changed src/build_models/testplugin.h
removed src/build_models/simplugin.h