Implement HTTPCheck to check HTTP sites.

Specify in request: url, type (get, post, header), custom headers
Check for return: status code, content in response text, headers

Currently all fields do not have specifications of their max lengths. This should be added accordingly.

Explain

• Worker
• Notifiers
• Getting started

run_master and run_worker, both of which are outside the gefion package, contain code that perhaps would be better if they were in the actual package.

Currently individual loggers initialised with name are provided but not used. They should be ccalled instead of the global logging functions.