Fix startup message
Remove Streamline.js cache before service startup

Observed issues with stale cache.

/cc @aseemk
Run without `sudo` to preserve special environment variables

For example `PATH` and `LD_LIBRARY_PATH` are reset, although they are required
for `vips` to run properly. Setting `sudo -E` flag to preserve environment
doesn’t resolve the issue.

TODO: Find out what the best practice is.
Define language for syntax highlighting
Do not install `imagemagick`
Bump `deepzoomtools` to 0.0.4

Allows us to catch error when tile directory already exists.
Detect if ID has already been created
Run as admin user

Previously, we actually ran as root which is less safe than running as admin
user with less privileges. Include path to VIPS binary in `PATH` environment
variable to ensure we have the fastest DZI generation.

See: 7367f5e99879029b1b752ac8c8014c1342aa2998