Location: Convert hook_theme() and related theme functions

[ddrozdik]

Blocker: #20
Let's convert hook_field_extra_fields() into Drupal 8 format.
Additional information:

• https://www.drupal.org/node/2231673
• https://www.drupal.org/node/2100775
• https://www.drupal.org/node/1805952
• https://www.drupal.org/node/1876710

Which theme functions should be converted:

• location_settings
• locations
• location
• location_latitude_dms
• location_longitude_dms
• location_element
• location_distance

these two theme functions are removed in dmaps:

• location_map_link_options
• location_geocoding_options