wip: repository_manager: add suffix on completing file path
wip: repository_manager: add installed repository management methods

* add @installed_repos_db
* add @installed_repos
* add init_installed_repos()
* add load_installed_repos()
* add save_installed_repos()
* add add_installed_repo()
* add remove_installed_repo()
wip: spec_helper: add fakefs_helper to be always enabled FakeFS
wip: spec/test: remove FakeFS.[de]activate! from test scripts