Add FINEST debugging and fix #153
Update README with info regarding non-PR refspec

Using the default `refspec` prohibits the project from automatically building non-PR branches like `origin/master`. Prepending the `refspec` with the heads and remote/origin allows the project to build pull requests as well as other branches like `origin/my-feature`. This should resolve #77.

Big thanks to https://github.com/janinko/ghprb/issues/77#issuecomment-40400379 :smile:
Merge pull request #168 from justindowning/patch-1

Update README with info regarding non-PR refspec
Merge pull request #166 from nocturo/bugfix/triggeronly

Add FINEST debugging and fix #153
[#160] Add build-flow plugin as dependency
[#160] Extract buildURL calculation to a method
[#160] If build is from FlowRun type, then iterate through its jobs graph adding all downstream jobs build urls to the message that will be posted to github pull request.
[#160] Make build-flow dependency optional, as suggested
[#160] Define an interface to calculate build URL, implementing a default behaviour
[#160] Implement BuildFlow build url calculation
[#160] use a factory to decide which downstream manager to use
[#160] Apply factory to the place where URL is calculated to be sent to github
[#160] Prevent that the plugin is not installed, returning default behaviour instead
[#160] Forgot author
[#160] Add javadocs
[#160] Rename interface and base class with better names
[#160] Rename factory to a better name
[#160] rename BuildFlow to a better name