build: use powerline for terminal prompt

[rokroskar]

Prettifies the terminal shell with powerline.

screenshot:

closes #31

[emmjab]

this is awesome! tested here: https://dev.renku.ch/projects/e.jablonski/base-docker-image-tests at commit 4e3194ce.

The coloring & characters for commits might help solve the open issue about helping users realize they need to push more often.

[rokroskar]

Thanks for testing @emmjab - btw, do you have powerline fonts installed on your computer already?

[rokroskar]

I resorted to using the "compatible" mode that results in an uglier font but the alternative is requiring that the user installs fonts on their system, which I think is a no-go.

[rokroskar]

I just changed all the image builds to use compatible mode and to not install any fonts. Please re-approve.

[emmjab]

Thanks for testing @emmjab - btw, do you have powerline fonts installed on your computer already?

Nope!

I just changed all the image builds to use compatible mode and to not install any fonts. Please re-approve.

Re-testing now.

Also I agree it would be nice to have a common/ dir for dependencies that all the images share, in a following PR; so long as we make it clear what's going on in the docker file.

[emmjab]

👍