Create a stable release of locationmap for Drupal 8

I've started a Drupal 8 port in the 8.x-2.x branch. This has the main admin form ported to use CMI and the main page reads from a $config object. There's more to do though, like the blocks, setting default filter formats on install, etc. Over time I'll add other issues for those tasks (of it others would like to, feel free) and use this issue as a meta issue to track what we need to do to produce a stable release for D8.