[hotfix] move splashsite to new provider

• modify inventories to include new IP for splash site

  • side-effect: label the hosts by the aliases used by our provider to make it easier to look them up in the provider's console

• use 0xacab registry image in splashsite docker-compose configs and docker build steps

  • move splash.dockerfile to top-level docker dir to reuse bin/docker-build (and make stuff easier to find)
  • provide make command for building/pushing splash image
  • cleanup: fix typo in signald.dockerfile

• modify splash deploy script to pull containers in prepare step (not build)

  • pull splash container from registry
  • pull LE image to make sure we are using most recent version of