Container image is larger than necessary

[simar0at]

Container images get smaller and easier to download the less layers they have. Combining some RUN instructions will decrease the size of the final download but increase build time as every change in a larger block of instructions will invalidate this whole layer.
Usually on an image that is not in heavy development anymore it is better to merge as many RUN and other Dockerfile instructions as possible.

[musicEnfanthen]

Fixed by #28