Issue #29: Unit Tests for coloredcoinlib and ngcccbase

coloredcoinlib
* Fixed some bugs in builder.py, particularly AidedColorDataBuilder
* Removed __gt__ for comparable mixin since it's defined in the two subclasses
* Fixed explorer.py to use the BASE_URL
* Removed from store.py get_persistent_dict which nothing was using
* added test_builder, test_store, test_toposort
* Now covers everything except about 5 lines in all of coloredcoinlib

ngcccbase
* added tests for services/*.py
* added tests for wallet_model