clean up concurrent output of tests

clean up concurrent output of tests

Using concurrent-output this is easy. Just have to check if tasty has
color enabled, and propagate it into the worker processes, some of which
will be run without a controlling console.

Also added a call to installSignalHandlers; I noticed that interrupting
the test suite could leave the console in a bad state and this fixes
that.

The ansi-terminal dependency is free, since tasty also depends on it.

Sponsored-by: Dartmouth College's Datalad project