Sorting import statements was made easier and less error-prone using [isort](https://pypi.org/project/isort/)
Make it clear that the `yaml` package is not part of Python's Standard Library and should be installed with a package manager as outlined in [this](https://pep8.org/#imports) section of PEP8.
This applies to the Walking Corpse in particular, which has 4 MP and 4
movement cost to enter shallow water. In practice this means that it can
move into shallow water only if it's not slowed and hasn't spent any
movement points this turn, and then it cannot move any further until the
next turn.
Closes#5689.
The following line was causing a wmllint error because it contains _s:
Irs, book_start Icr^Ii, Irs
"../../data/campaigns/Descent_Into_Darkness/maps/07c_A_Small_Favor3.map", line 10: warning, fog or shroud in map file
As far as I can tell this lines do nothing.
1. `file_handle = None` is NOT how to close a file in python
2. The file handle is already closed due to `with open() as file_handle:`
A comment containing a string [advancefrom] was causing wmllint to get confused
../../data/campaigns/Dead_Water/scenarios/06_Uncharted_Islands.cfg, line 22: [advancefrom] needs to be manually updated to [modify_unit_type] and moved into the _main.cfg file
wmllint saw [side] inside a comment and incorrectly assumed it is reading a side definition
"../../data/multiplayer/scenarios/4p_A_New_Land.cfg", line 484: side number 5 is out of sequence (11 expected)
"../../data/multiplayer/scenarios/4p_A_New_Land.cfg", line 488: side number 5 is out of sequence (11 expected)
"../../data/multiplayer/scenarios/4p_A_New_Land.cfg", line 512: side number 6 is out of sequence (11 expected)
"../../data/multiplayer/scenarios/4p_A_New_Land.cfg", line 516: side number 6 is out of sequence (11 expected)
"../../data/multiplayer/scenarios/4p_A_New_Land.cfg", line 540: side number 7 is out of sequence (11 expected)
"../../data/multiplayer/scenarios/4p_A_New_Land.cfg", line 544: side number 7 is out of sequence (11 expected)
"../../data/multiplayer/scenarios/4p_A_New_Land.cfg", line 568: side number 8 is out of sequence (11 expected)
"../../data/multiplayer/scenarios/4p_A_New_Land.cfg", line 572: side number 8 is out of sequence (11 expected)
"../../data/multiplayer/scenarios/4p_A_New_Land.cfg", line 805: side number 1 is out of sequence (11 expected)
"../../data/multiplayer/scenarios/4p_A_New_Land.cfg", line 818: side number 2 is out of sequence (11 expected)
"../../data/multiplayer/scenarios/4p_A_New_Land.cfg", line 831: side number 3 is out of sequence (11 expected)
"../../data/multiplayer/scenarios/4p_A_New_Land.cfg", line 844: side number 4 is out of sequence (11 expected)
