Code licenses

[peastman]

It looks like a lot of the code here is copied directly from other repositories, but it doesn't include any license notices.

[rbharath]

Yes, my bad, was meaning to copy those in later. I believe the current sources of code are as follows:

• DeepChem contrib (the fully connected networks and graph convs are from there).
• https://github.com/gmum/MAT: This is the molecular attention transformer code. It looks like there isn't a license in that repo. I'll raise an issue there and link here to track.

[rbharath]

I've raised an issue at ardigen/MAT#5.

[rbharath]

MAT just added a MIT license so both our sources are MIT licensed. I'll add an MIT license to this repo in a future PR