Docker changes and optimisations

[kawaii]

Some small yet quite important changes. All tested and documented below:

• Removes the redundant mkdir /opt/camo layer of the Dockerfile since WORKDIR makes the directory if it doesn't already exist.
• Adds a .dockerignore file and changes 3 ADD layers into a single one with the same effect.
• Bases the image from Alpine Linux (still an official node image) to greatly reduce the size and attack surface of the image/container.

[kawaii]

I've pushed another commit, ccaacf5 - which was a change already proposed as part of PR #134. Figured we could hopefully kill many birds with one stone.

[rmm5t]

@kawaii node-8.16 is now the latest node 8 version.

[kawaii]

@rmm5t thank you for informing me of this, I simply based my commit from your earlier PR without checking Docker Hub for updated information. Perhaps it would be best for us to test the application under a more modern Node.js version such as 11 or 12?

[rmm5t]

Odd numbers are unstable versions. Version 12 was just released this week. Node 10 is probably the most appropriate for now.

[kawaii]

I've made some more pushes with some general quality of life improvements to the Dockerfile, such as using COPY instead of ADD as suggested by Docker Captain @bretfisher! :)

[kawaii]

Bump! Anyone with merge powers able to check this over? :)

[kawaii]

Screams into cyberspace, but no one hears.

[wallopthecat]

This really should be merged. Thanks, using your fork in a project now