Contributor project

This introduces a contributor project, **org.eclipse.buckminster.contributor**.
The aim of this project is two-fold:

- provides a **workspace.cquery** that introduces in the target platform some source bundles (at the moment org.eclipse.sdk for all eclipse bundle sources and egit.core.source); this cquery is thought to be used for materializing the Eclipse workspace; having source bundles in the TP allows to inspect the sources of all used libraries.  I found this much convenient in the past to contribute patches to Buckminster.  In fact, the current build.cquery in releng project only materializes binary dependencies for the build where source bundles are not required.  The cquery uses the releng rmap, so the delta is minimal.  The buckminster.cspec in the contributor project has a dependency on org.eclipse.buckminster.releng, thus it basically materializes a TP which is a superset of the TP used by the releng project.

- provides a **build.ant** script so that one can run the headless build in his own machine a create all the artifacts (p2 repository) in his machine.  This ant script also automatically installs the buckminster headless for performing the build, thus it is rather easy to use (even from the Eclipse workbench).  It has a custom properties file and reuses the bmscript file in the releng project.

The instructions on the wiki could be changed accordingly so that in the Eclipse workbench one opens the remote workspace.cquery instead of the build.cquery.

Personally, I've used this strategy in the past when preparing patches to contribute to Buckminster.