Improve API usability by simplification of some endpoints

[Crsi]

• Remove the active field for POST /refunds (they should always be enabled)
• Remove the active and participants fields for POST /communisms (they should always be enabled; the creator of a communism should automatically join it with the quantity 1)
• Add a field to POST /polls/abort containing the user alias of the user that issued the command to enforce user permission checking on the API server
• Add a field to POST /refunds/abort containing the user alias of the user that issued the command to enforce user permission checking on the API server
• Add a field to POST /communisms/{close,abort} containing the user alias of the user that issued the command to enforce user permission checking on the API server
• Remove the endpoint POST /communisms/setParticipants
• Add two new endpoints POST /communisms/increaseParticipation and POST /communisms/decreaseParticipation, both with the body of the communism ID and the user ID or user alias that should be increased/decreased (to finally replace the POST /communisms/setParticipants call above)
• Remove the GET /ballots endpoint, if no specific usage is found
• Remove the GET /multitransactions endpoint, if no specific usage is found
• Remove the GET /votes endpoint, if no specific usage is found (this endpoint is necessary)
• Change the DELETE /aliases endpoint to only require the ID of the alias in the body
• Change the DELETE /callbacks endpoint to only require the ID of the callback in the body
• Replace the PUT /aliases endpoint with a POST /aliases/confirm endpoint
• Replace the DELETE /aliases endpoint with a POST /aliases/delete endpoint
• Drop the PUT /callbacks endpoint
• Move the functionality of the POST /transactions endpoint to accept consumption requests into its own new endpoint POST /consume (or similar name)
• Remove the POST /users/setName endpoint after #105 is done
• Rename the POST /users/disable endpoint to something like POST /users/delete or similar (note that this is a soft delete on the server, therefore the HTTP method DELETE isn't used)
• Add a new field to the POST /users/disable endpoint (or similar name, see above) containing the user alias of the user that requested to disable the mentioned user (the user ID should not be replaced) as a way to enforce permission checking in the server instead of the application code
• Remove the fields voucher_id, external (use default) and permission (use default) from the POST /users endpoint, so that this endpoint has literally no required body at all