- Refactored to use extension model

Hi,

I refactored semantic-versioning-plugin to use extension point model so it can be extended with new semantic parsers in example ANT-parser.

I also refactored Pom Parser to resolve build file (pom.xml) from given root pom parameter, because at least in our build pom.xml locates at /<workspace_root>/workspace/<project_name>/pom.xml folder

and third and last modification is that now it is possible to select which parserer is used in that particular build job.