compute bond angle cosines inside ALIGNNAtomWise.forward to ensure al…

[bdecost]

this PR addresses autograd forces in ALIGNNAtomWise, in light of discussion at #113

• moves autograd toggle on relative displacement vectors to the start of ALIGNNAtomWise.forward
• re-computes bond angle cosines inside ALIGNNAtomWise.forward to make sure angle terms are definitely included in the autograd trace

[knc6]

Hi @bdecost

Currently, I am testing the on the fly line graph option. We can make it as default soon if it works out.