move similar functions to common.js

[JRJurman]

Probably don't need this, but if you wanted to make more significant changes, this might be worthwhile

[ethanjurman]

While this abstraction does move functions that are similarly named together, it ultimately makes it harder to work in a single project (you having to open multiple files at once to work on a single page).

I think if we do end up abstracting the code, I'd like it to be in a way that thematically fits the application- like a section for board logic and a section for the letters at the bottom.

I'm gonna mark request changes, but I don't truly think this work is necessary- so don't feel pressured to update it, and feel free to close it.
I might steal the readme part tho- that's an oversight on my part (not including a development section)