Feat/103 assign task4 ddfs

[astim1]

Converted assign_TASK4_DDFs() from R to python and added a test script for it in tests.

The test required me to convert most of section 3a of Main(), as well as a couple other attribute maps earlier in the script, from R to python, so this could be used when time comes to implement that part of the main function in python.

[rroyall-stantec]

I would suggest rather than declaring a bunch of work inside the actual test function, look into pytest fixtures and use that to set up the input values instead. Technically we should be using fixtures for reusable code blocks and input variables for tests but it also allows us to not pollute the test function itself with tons of setup code that isn't doing any actual testing.