Add micro text editor to default image
Add micro text editor to default image

Adds the `micro` command-line text editor as a default, that should be friendlier than vim to newcomers who find themselves in a text editor unexpectedly (such as when making a git commit).
berkeley-dsep-infra/datahub,ryanlovett/datahub,ryanlovett/datahub,berkeley-dsep-infra/datahub,berkeley-dsep-infra/datahub,ryanlovett/datahub