Create a new variable to hold branch name of the project scm

The configuration parameter 'projectNameTemplate' is able to use the following strings to define the project name pattern: groupId, artifactId, version. When using a pattern ad '[artifactId]-[version]', it is needed to re-generate Eclipse files when changing the version. To avoide this re-generation, I think a new variable [branch] holding the SCM branch name or "trunk" should be added.