Add support for multiple sigels

[sweco-semhul]

Both kitin.py and angular app lacks support for multiple sigels.
Related to issue #224
Example for user test:
{"username": "test", "email": "[email protected]", "authorization": [{"sigel": "SEK", "ill": false, "reg": true, "kat": false}, {"sigel": "SBD", "ill": false, "reg": false, "kat": true}]}