feat: extend consent management api

Introduces 2 new API endpoints to proxygui to be used by Perun for consent management by user:

• GET /users/me/consents endpoint for listing all user's consents in proxy db
• DELETE /users/me/consents/<consent_id> endpoint for deleting a specific consent

closes PRX-286

perun/proxygui/api/oauth_api.py

@@ -23,7 +23,6 @@ def construct_oauth_api(cfg):
 
     @oauth_api.route("/authorize")
     def oauth2_authorize():
-
         # generate a random string for the state parameter
         session["oauth2_state"] = secrets.token_urlsafe(16)