Start GZipping facia-press pressed files

This starts putting `pressed.json` files compressed in `GZip` format.

In order to read them, `WS` needs `ws.compressEnabled: true` in `application.conf`; after which it can then read naturally.
Browsers can still view the files as they have the header `Content-Encoding: gzip`.

For `/uk` on `DEV`, I have seen a decrease in filesize from `1.9MB` to `502KB`.

@stephanfowler @robertberry