move icon classes from themes/__init__.py to config/default.py

[RogerHaase]

In themes/__init__.py there is def get_endpoint_iconmap that mirrors item_views in config/default.py. A few lines of code could be saved by moving the fontawesome classes from __init__.py to default.py.

Given the arbitrary choices made for some icons, some wiki admins may want to specify a different icon. That cannot be done now without a code change.