Show build status more clearly

[hamvocke]

Currently burstah shows build stages in one of three colors:

• Green, if the last build was successful
• Red, if the last build had an error
• alternating colors for everything in between

Go knows multiple different status for build steps, e.g. assigned, in progress and so on. Burstah would be more helpful, if it'd try to show these different build status with a designated color. At least it should show, which build step is currently in progress.

[lplotni]

Do you think it got better since 63f5564 as we now visualize the state of the previous build?