project_tools.sh broken on MacOs

[imoldfella]

Explained in detail

I can submit a patch, but wanted to discuss the appropriate way. I suggest changing project_tools.sh to use python3, and checking for its existence, then changing add-line.py to print(...) instead of print.

Obviously there is more than one way to do things, but this seems to be the approach of least surprise and doesn't encourage users to install EOL software.

Thoughts?

[imoldfella]

This is also broken on Mac because of this
This requires editing the Podfile and a little dance with Xcode. There's probably a way to edit the .xcodeproj without using Xcode, but I haven't attempted to figure that out.