Change routes to use POST Requests for payment actions

[Kilobyte22]

Currents the Actions deposit, payment and buy use GET requests. This change adopts it to POST requests.

The API has gotten a new Version v2 which uses POST Requests.

Except for the API change, this has been running successfully at Das Labor for a couple of months

Open Questions:

• Is this worth a new API version? Maybe just add the POST requests to the exisiting version

[marudor]

I'm fine with adding v2 APIs incrementally. @YtvwlD?

[YtvwlD]

Well yes, but this API is not our planned v2.

I'm fine with merging this in general, but this broke non-js usage (because the buttons then do GET requests)

[Kilobyte22]

but this broke non-js usage

This should be fairly easy to solve by adding additional GET routes which would just display a small two-button (OK/Cancel) form. Its not quite as nice UI-wise as previously but it would allow people without JS to use it. I might look into this later, this shouldn't be too difficult

I believe we actually already talked about this in person a couple of months ago

Edit: It might also be feasable to turn the buttons in the UI into actual html buttons, so they could send POST requests without javascript help. I don't know my way around webdev too well though, so I'll have to figure this out

[marudor]

For post requests without JS you need to make a form out of it. Then let the form submit a post and the button is the submit for that form