Anonymous proposal submissions blocked when group limit reached

[simonaszilinskas]

Describe the bug

Anonymous users cannot submit a new proposal once the limit of proposals that can be published by a user (or a group) to a Proposal component has been reached.

This is because the feature enabling anonymous users is based on the creation of an ‘Anonymous user’ user group. The problem is that when an admin set a proposal limit per participant, this also affects user groups. Then, once this limit has been reached for the anonymous users group, signed-in users cannot publish a proposal anonymously and non-signed-in users cannot go through to the end of the publication step either. 

To reproduce

• As an admin, create a Proposal component and enable anonymous proposals. Set a proposal limit per participant (for example 2 proposals).
• As a signed-in user, create and publish two proposal as an anonymous user. 
• Try to create a proposal once again: see that you cannot publish it. 
• As a non-signed-in user, try to create a proposal as well: see that you cannot publish it.