Add button to allow uploading a file

[ajgeiss0702]

This PR only effects the front-end UI.

Easier to upload a file, especially for large data.

I plan to have this on my own hosted instance of bytebin with a larger size limit, and thought it might be useful for others too

If you are against changing the button text, let me know of any alternatives. I thought about it for a bit, but this way made the most sense. Clicking the upload button opens a file select box. The previous upload button was renamed to "save"