Structure refactoring

Renamed checker modules:
heartbeat/checkers/build_version.py →heartbeat/checkers/build.py
heartbeat/checkers/python_version.py → heartbeat/checkers/python.py
heartbeat/checkers/redis_status.py → heartbeat/checkers/redis.py
Please take this into consideration when setting your HEARTBEAT 'checkers' configuration in your project's settings.py

Refactored json response structure for the 1337 endpoint.
For more details: 309b8b0