Cleans up Makefile.
Adds first version of foreign key caching. Not yet working correctly.
Fixes issues with cache. Default cache time: 2 minutes.
Updates icons.
Re-structures dbnavigator into modules.
Re-organises into modules.
Re-organises tests. Puts postgres specific code into the postgresql module.
Makes database sources modular.
Makes databaseconnection more flexible.
Adds more tests.
Adds a mock service to test database abstraction.
Adds info when table comment is not overly correct.
Adds sqlite database driver.
Adds SQLAlchemy as database layer.
Uses more features from SQLAlchemy.
Updates autocomplete strings and expected testcase values.
Re-structures tests.
Moves mock source to test sources.
Merge branch 'feature/sqlalchemy' into develop