Add a linter for manifest file

[cbeauchesne]

1. check if entries are sorted in test_the_test (can be removed if 3. is done)
2. check for items existence in test_the_test
3. automatically sort entries in format.sh if the option --check is not set. Fail otherwise if the file would have been sorted
4. format file in format.sh if the option --check is not set. Fail otherwise if the file would have been reformatted

[dmehala]

@cbeauchesne just to be sure, what's the difference between automatically sorting entries and format file?

[cbeauchesne]

Format is about using tab/space, size of tabulation, using quotes/double quotes ...
Sort is only the fact that list items and dicts keys are sorted.

Both could be seen as "formatting", but they will probably be addressed by different tools. Though, if a tool can do both, that's perfect.