Configuration Implementation/Layer Mapping

Couple of autotools corrections in here, but main bulk is redoing the configuration loading from yesterday to only deal with a single file (`DEFAULT_CONFIGURATION_FILE`). Also note this was tested by slightly modifying set_string in src/cli/main.c and running a command. "make check" isn't a good test case here, so we should indeed migrate to real functionality testing via buxtonctl. 

We also need to plan some `atexit` implementation as our cleanup hooks for library exit, or at least add a teardown method called from buxton-daemon and buxtonctl. Thankfully the hashmap's make it that bit cleaner and easier to manage. This is the last set of changes required to push a working backend in for testing.