ignore MAC meta files on import and also remove any such files from the ...

...course

STUD-1725
@waheedahmed @symbolist @adampalay 
To allow DevOps to override this setting via a JSON file, need to add the following line in `cms/envs/aws.py`:

```
ASSET_IGNORE_REGEX = ENV_TOKENS.get('ASSET_IGNORE_REGEX', ASSET_IGNORE_REGEX)
```