Add releng component for building with buckminster

This enables mirroring of the p2.site using p2 actions from buckminster
This file also contians extra dependencies needed to build the bundles in this repo
Updates bundle versions to 2.6.1
Feature version set to 2.6.1
Make a synced refresh of workspace before reading generated file

Solves bug 3563
Merge branch '2.6.1' into develop