Changed ILS driver loading sequence for more flexibility. No hard work is...

Changed ILS driver loading sequence for more flexibility.  No hard work is done in the constructor; instead there is an init() method that gets called by the VuFind\ILS\Connection class.  Additionally, drivers no longer load their own configurations; instead, configs are pushed in by VuFind\ILS\Connection, making reuse easier in other contexts.  Finally, ILS drivers all inherit from the same base class, easing future functionality.

PICA configuration now includes copy of DAIA settings -- this avoids the need to load two separate configs when using PICA.ini

Fixed a Symphony namespacing bug.

Stub tests have been added for all existing drivers, though they do not cover much code yet.