Change logger for zinc

[jvican]

I want colors, highlighted stack traces, nicer way of reporting log levels, and a simpler logger architecture than the one that sbt has.

[olafurpg]

From utest

  /**
    * Whether to use SBT's test-logging infrastructure, or just println.
    *
    * Defaults to println because SBT's test logging doesn't seem to give us
    * anything that we want, and does annoying things like making a left-hand
    * gutter and buffering input by default
    */
  def useSbtLoggers = false