Consider moving all applications' docker images to imageStreams

[jmaupetit]

Purpose

As discussed in [1], using imageStream objects instead of raw images allows substantial optimizations to decrease network bandwidth (while pulling docker images), add monitoring to our applications, or customize our builds (e.g. add a theme for edxapp, etc.).

Proposal

A first POC for edxapp has been implemented in #105, this should be generalized to all distributed apps (at least richie and hello at the time of writing).

References

[1] #101 (comment)

[jmaupetit]

Already fixed.