Support more than just git as project-root

[addiks]

Currently it is to be expected to use git to manage the projects as the project-index will be put into the ".git" folder. If the project does not have such a folder because it does not use git (or even has the repository in a different, maybe outside, folder) then this plugin can currently not be used with that project.

It should be possible to use other software (like svn, etc) as a project root and as a fallback just ask the user where to put the index for this project or just use it's own hidden folder.