Remove obsolete openproject-plugins dependency

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Remove mention of openproject-plugins in README

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Remove superfluous comment in engine.rb

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Merge pull request #105 from finnlabs/feature/integrate-op-plugins-plugin

Remove obsolete openproject-plugins dependency