Geocoding improvements

I want to make some improvements to the geocoding & searching:

1) Remove hard-coding of geocoder to google in proximity custom search

2) fix proximity custom search to work with smart groups. Currently you can filter by normal groups and it works but smart groups don't. Since there is working smart group filters in the main search AND working proximity filtering in the main search I want to make it closer to the main search. 

3) allow a geocode to be entered (if known) instead of an address (custom search & advanced search)

4) add unit tests to proximity searching

5) remove the multiple attempts to geocode on the custom proximity search

6) I am reviewing & picking up some of the open geocoding tasks. However, I won't do any fixes to the Google geocoder class that ships with core as I am expecting that to be replaced with an extension class

https://issues.civicrm.org/jira/issues/?jql=labels%20%3D%20geocoding%20and%20resolution%20%3D%20Unresolved%20AND%20project%20%3D%20CiviCRM