GH95 - custom icons

#95
lets move this method in mindmap project
create MindMapService, register it, and add there this method

rename method to getRepositoryCustomIcons(String repoPath) 
-> this method must return ALL icons from folder structure (not only direct children)
-> the result must contain the entire path, not only the name (e.g. user/repo/mindmap_icons/....png)