remove all buildout_* files to make things easier to understand/customize

Its not clear why we need the customization  buildout_*cfg  files to include all the dependency buildouts (lxml, solr,..).  Also disabling dependencies is complicated. 
We already had some discussion about this, mainly in  #232.

I propose to:

* remove all buildout_* files
* instead include the needed dependency buildout files directly in buildout.cfg