Remove pylab star import in labscript.labscript

[dihm]

As discussed in #102, it would be good to remove any and all star imports, especially pylab which is largely deprecated and brings in a ton of junk to the labscript namespace.

A hurdle to this is that users are likely accidentally relying on some of these imports in their scripts. If we wanted to avoid a breaking change, we could just go through and manually import the useful stuff that pylab brings (even if we aren't specifically using it within labscript). Though it is probably better to just pull the bandaid and even update the docs to discourage the from labscript import * idiom.