Rewrite linter and add support for linting configuration

[Zethson]

• We should refactor our linter so that we are not using a metaclass for every linter, which gets all in the python script defined linting classes, but so that the template linter just gets a list of imported linting functions and calls them. Those should then be more generalized
• Our linter should be configurable. I envision that the cookietemple.cfg file has a section [linting] where one can disable checks

[linting]
general-7
cli-python-2

• cookietemple lint should output a json or yaml file describing a summary of the linting results
• the pip package outdated requests should be parallelized Run linting requests async #494
• magic numbers should be removed in the check_section function
• Advanced: Improve efficiency of the linting by applying several linting functions while reading a single file