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• [ ] the pip package outdated requests should be parallelized #494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

[Imipenem]

• Improve efficiency of linting: Try to lint multiple things in on file and do not read it for every linting function

• Parallelize the pip package outdated requests (#494)

• Remove "magic number" in check_section function -> consider refactoring the pattern