Add ThemeRepositoryTest for the first time.

This test is unsolved test

1. call getAll method.
2. call get method.
Add ThemeRepositoryInterface
Add get method
Add ThemeRepositoryTest for the first time.

This test is unsolved test

1. call getAll method.
2. call get method.
Add ThemeRepositoryInterface
Add get method
Add exists method

Add getClassName method for get theme class name
Add theme exists test
Modyfy test case

Fix error message in get method when there is no theme
Modify get method test with adding exception test
Resolve conflict
Merge pull request #54 from toiee/feature-theme-repository

Create ThemeRepository