Bill entry screen refinements

Awesome app, thanks a lot! I would like to use that in favor of my current Tricount setup, but I realized that two small issues make my daily life a bit more cumbersome that necessary. Both are related to the fact that entering new bills should be quick, with as few clicks as possible.

1. The bill entry screen should probably rather be a form than a screen that opens modal input dialogs on demand. For each field to fill, this saves one click as users also need to confirm their entry each time.

2. The value of the "who paid" field should be a per-device cached value. It's unlikely to change for a specific mobile, and not having to enter it also saves one step.