Convert specs to RSpec 2.99.0 syntax with Transpec

This conversion is done by Transpec 1.12.0 with the following command:
    transpec

* 4 conversions
    from: obj.should_receive(:message)
      to: expect(obj).to receive(:message)

* 1 conversion
    from: obj.stub(:message)
      to: allow(obj).to receive(:message)
Convert specs to RSpec 2.99.0 syntax with Transpec

This conversion is done by Transpec 2.3.1 with the following command:
    transpec

* 1 conversion
    from: describe 'some controller' { }
      to: describe 'some controller', :type => :controller { }

For more details: https://github.com/yujinakayama/transpec#supported-conversions
Adapted gemsepc dependencies to new version scheme
Remove obsolete openproject-plugins dependency

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 #2 from finnlabs/feature/integrate-op-plugins-plugin

Remove obsolete openproject-plugins dependency
Merge pull request #1 from finnlabs/feature/rspec-299

RSpec 2.99 Upgrade
Adapt version to corresponding OpenProject core version.
Update stable to v4.0.0