api.py: Fixes reloading config file for remote_db

When calling an api function such as .get_available() you would
previously not get any custom overlay definitions listed in the
output, in order to fix this the config gets reloaded when the api
attempts to obtain the remote db.
config.py: Adds output attribute for OptionConfig
layman_.py: Adds repo installation

If a repository is specified in the repos.conf config file and it
doesn't exist in the list of installable overlays an overlay.xml
definition will be created for that overlay and it will be
installed.