Remove use of GNU date extensions when labeling images ...

Fixes #197

Merge branch 'fix-skip-git' of https://github.com/mattolenik/netbox-docker into mattolenik-fix-skip-git

Respect SKIP_GIT environment variable when building ...

Fixes issue #190

Adds more labels to the Dockerfile ...

It also updates the README and the bug_report template to reflect
the changes. Additionally, in the README some relevant shields from
shields.io are added.

The labels follow [label-schema.org][lsorg] and the [OpenContainer
image spec, section annotations][ocis], specifications.

[lsorg]: http://label-schema.org/rc1/
[ocis]: https://github.com/opencontainers/image-spec/blob/master/annotations.md

Corrections for shellcheck warnings

Update purpose text in build.sh

Fix build ...

The Docker Hub build system runs on Ubuntu Xenial containers.
Xenial's git is 2.7.4, which does not know the `-P` flag yet.

Checkout the repository with git ...

This changes the build process even further. Instead
f using `wget` to fetch the current code, `git` is used.
This allows for faster switching between branches,
because only the differences between them have to be
fetched from the server.

But the main advantage is that the build cache can
finally be used as designed by Docker. Repetitive
builds are very fast now. This is also true between
branches and tags, as long as the `requirements.txt`
file doesn't change.

externalize netbox download with wget

Fix caching in build.sh

Only build the master branch to speed up the test

Refactor to multistage builds ...

This commit introduces a huge change in the build process.

What changed:

- Dockerfile.ldap was integrated into Dockerfile as a seperate
  [build stage][multistage-build].
- All the build scripts were refactored according to this.
- The `docker-compose.yml` file was adjusted likewise.
- The main build script, `/build.sh`, now always builds all
  targets (formerly called variants).
- The minimal requirements for Docker and docker-compose
  have increased.
- The build on hub.docker.com must be adjusted.

This change should also fix #156 permanently.

[multistage-build]: https://docs.docker.com/develop/develop-images/multistage-build/

%s/digitalocean/netbox-community/gi ...

Thank you Digitalocean for sponsoring Netbox!
And thank you for letting it grow up and move out ;)

reorganized tagging

Add short version tag ...

Adds a short version tag in the form of v$MAJOR.$MINOR. This tags
creates the possibillity to follow patch releases automatically with the
scheduled import option in Openshift and Kubernetes.

Fix default in build.sh

Update references to netboxcommunity

Build system for hub.docker.com

Revert "⚙️ Print every command" ...

This reverts commit 1fb6b80.

⚙️ Print every command

⚙️ Additional build debug info

Add proxy support to build.sh.

✨ Introduces a Netbox Docker project version

✏️ Typo

🐞 Fix parameter passing

🐳 Allow variants from other source images

❇️ Adds DEBUG option

💄 Cleanup and hide warnings

Add django_ldap_auth ...

In the ldap.Dockerfile the django_ldap_auth module is installed to
enable authentication againt LDAP servers.

❇️ Adds new options to the build script