Persist repository and pr id from analysis report to database

Github Pull Request id and repository are specified as analysis command line arguments (see BRANCH-8 and BRANCH-9).

We need this information to be persisted into database so they can be used later when a change in the UI implies PR decoration to be triggered again.

One option is to provide a way for the branch plugin to declare these new properties to be persisted along the "sonar.analysis.*".
One other is to persist this information as new columns/new table associated to the analysis.

These properties are defined by the branch plugin, supporting directly these properties in the core is therefor discutable.