Overhaul docker-build and docker-push scripts

[tsvi]

This project needs an overhaul when it comes to building images anyway. We use hassio- addons/build-env but that project has been archived. There must be a better way for us to do the bulds.

Fixing this would likely just require updating these two scripts. https://github.com/d0ugal/hassio-dropbox-upload/tree/master/scripts

If somebody can figure out how other projects are handling this I would be happy to try and update.

Originally posted by @d0ugal in #49 (comment)

[tsvi]

See #49 (comment)

The hassio-addons repo now uses the following script which uses the Gitlab CI for creating docker images:

https://github.com/hassio-addons/organization/blob/master/gitlabci/addon.yml

Each addon has its own .gitlab-ci.yaml (see eg. https://github.com/hassio-addons/addon-ssh/blob/master/.gitlab-ci.yml)