Review default values for frontend

[pkraker]

There are a number of problems with the default values that were introduced to the frontend:

• They are all included in the localization, even though most of them are not displayed to the user.
• They currently mask problems/errors in the backend. Example: #167 would have been earlier discovered, if the default year wasn't set to 2017.
• Default value for year does not work with filter/sort (see #167)