Add Exif dependency

(cherry picked from commit d3431628b3c8970cad48e83c2b0bce80829910b3)
Add check to ignore empty sites dir

(cherry picked from commit 4834259dcb95eaaee8d3bc671466541ab5601b87)
Install whole erlang package, something was missing.

(cherry picked from commit 6cc6bb629661359b9dda3c60180a81a36ba188b4)
Switch back to debian. Smaller and builds faster.

(cherry picked from commit 3bbc547e1df79919aa86b68182c08d1831db7bbf)
Run tests on build.

(cherry picked from commit 5c9dd3aff504090d0f88d87d1769f3c29829cf74)