Add persisted media lookup

Adds http/routes/get_hilite_media.ex which allows HEAD and GET of persisted media.

Persistence & Email ingest

Adds persistence and email ingest support.

Bumps app version to 0.2.0. API version remains the same as the surface the extension uses has not changed (only POST /sns has been added).

v20220126: First major commit of elixir daemon

Pre-built release package for Ubuntu 20LTS attached here as hlte-20220126-ubuntu20.zip. Run simply with hlte/bin/hlte start.