Remove surefire sensor

In order to move out the plugin from the java ecosystem, the SurefireSensor is dropped
as its information are not the most relevant.
Drop dependency of sonar-cobertura-plugin

The trigger of cobertura via maven is now dropped.
The parsing of reports is done directly in the plugin and does not rely on any external library.
A property to specify the location of the cobertura report has been added (required to parse the report)