Refactor configuration

1. Refactor conf.py
2. Refactor post_processors.process + processors.process and their usage
3. Modified test settings
4. Refactor thumbnails.utils.py parse processors to adhere to new configuration
Refactor conf.py and post_processors.py

1. Fixed wrong default for PROCESSORS and POST_PROCESSORS in conf.py
2. Use direct access to array instead of using get method
Refactored PATH -> processors when parsing size dictionary
Typo, `processors` => `processor`
Merge pull request #53 from SeiryuZ/configuration-refactor

Refactor configuration