Add support for patch_base_image when not running locally

[jprokos26]

Addresses #1930

Searches for patch_base_image in more than one place:

1. Check if file exists in module path
2. Check if file exists in armory.paths.runtime_paths().cwd
3. Check if supplied patch_base_image is actually a url to an image we can download
   Else fail

[jprokos26]

Whenever I tried to pip install -e . with these changes and move to a different directory when I launch the docker container the armory being run does not have these changes so I was unable to test that the cwd gets mapped properly to runtime_paths().cwd when running as a pip installed package not locally.

[christopherwoodall]

LGTM!