Add birthday as readonly field to edit profile page

Job Doesburg
2019-10-03T17:08:49+02:00

/label ~bug

Closes #927

#### Previous behaviour
Steps to reproduce:

1. Open the profile edit view
2. I have no idea what my birthday is in the database
3. I can hide/show my birthday but don't know it exists

#### New behaviour
Steps to validate that it works:

1. Open the profile edit view
2. I can see my birthday in the database
3. I can hide/show my birthday and I know it exists