Add Tycho build system.

This is a working tycho based build system which doesn't interfere with
the old one. 
Use by calling `mvn clean verify` in the top level directory of the git
clone, a usable p2 repository will be available in
features/org.python.pydev.p2-repo/target/org.python.pydev.p2-repo-${version}.zip

Change-Id: I0677ab2cdac4971c2291d6ff68ea479f5bdeef9b