/root/devtools should be moved to a bash/sh path instead

[tywrenn]

Currently, the devtools script is located in the root folder and is in a location where Windows Subsystem might have trouble executing it. If we move it to a folder that's included in .bashrc such as /usr/bin, then you can execute the script easier like this:
docker exec -i (container name) /bin/bash devtools build-themes.

We can make this a backwards compatible thing as well so it doesn't end up breaking what we wrote down already.