Adapted gemsepc dependencies to new version scheme
Remove obsolete openproject-plugins dependency
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 #1 from opf/feature/integrate-op-plugins-plugin

Remove obsolete openproject-plugins dependency
Bump version to corresponding core version
Update stable to v4.0.0