This does clean `public/assets` before running dev-server
which seems to be required when running webpack in a hot-reload
mode.

This additionally quiets and fixes some temporary directories
that should be stored in `/data`.

WEBPACK_FORCE_COMPILE defaults to `false` but the script checks for it
to be empty. We should be explicitly checking for the value to be `true` instead.

Previously we would be using `> file` (shell redirect),
but this is suspectible to race conditions
when starting multiple containers writing that file.

Using `sponge` allows us to soak up all input,
and atomic replace existing file.

This reverts commit 1f1ba794.