Better UI on uploading tracks?

@jon-haavie Uploading tracks is quite separate from downloading - something like with music apps. Downloading is for people with "players" (Sisyphus tables and Minis in this case). But uploading tracks to the cloud for either your private use, or sharing with others, is done through our Webcenter. There you create an account (which is different than the account you created when purchasing your Sis.) and can upload as many tracks as you wish, and decide whether they are private or shared. The "upload tracks" facility that appears only on the browser version of our app, is for uploading directly (locally) to your table, from the computer running the browser and storing the track file(s). This allows you to create track files using a variety of software, and then play them on your table / Mini privately. But sharing with the community requires using Webcenter.