Update subscribe methods to get params on backend by request body

[akellbl4]

Now we have methods like /email/subscribe, /email/confirm and these API methods implemented as POST and PUT. But now they are getting parameters from query string.

I think they should get params from request body because it is usual way to pass data over POST/PUT requests. Also, it will be good to send an email/token as is without URL encoding.

[paskal]

@akellbl4, the change is merged. Feel free to change the frontend calls to utilise the body. tkn became token in the body, and everything else stayed the same.

[paskal]

@Jaskon this one already has backend support as well, feel free to pick it up if you'll have time.