build: simplify the project

This speeds up the Eclipse build quite a bit since it only needs
to build the main bundle once.

Signed-off-by: Ferry Huberts <ferry.huberts@pelagic.nl>
build: remove the features & plugins directories after p2 generation

Since they are no longer needed after that.

Signed-off-by: Ferry Huberts <ferry.huberts@pelagic.nl>