[mms] Abstract Horde configuration parsing into Horde_Registry_Hordeconfig class.

The ultimate goal would be to directly use the config objects as the
global $conf object.  It would have 2 immediate benefits (besides the
general future benefits of OO flexibility in the future):

1. On-demand config file loading.  If the application configuration is
never used in an access, we would never have to even load the config
file.
2. Even if the config file is loaded, we would then have on-demand
loading per key.  Which is still a win - merging configuration
options in an application can be very expensive in an access that
switches application contexts (I've seen 5% of script times spent in
_mergeConfig).

For now, just take advantage of abstraction by explicitly converting to
array after generation.  Passes existing complex config parsing unit
test, so we are no worse off than before.
Fix status() handling
Cleaner when written this way
Use array_diff_key() here
Drastically reduce the calls to getValue().

Per xdebug, reduces self time in search() API call from 3% to < 1%.
(My test example - addressbook search in IMP - reduce # of getValue
calls from 1,514 to 112).