change systolic onlyWire setting into a :pipelineModule() function?

[jameshegarty]

Instead of having 'onlyWire' be a setting in systolic, change it so that the user has to explicitly call a :pipelineModule() function before codegen if they want the pipelining behavior.

if they don't call :pipelineModule(), it would behave like onlyWire. If they do something that can't be supported by the pipelining code, they would get an error when they call :pipelineModule().

This would better modularize the code. Currently, there are a lot of hidden dependencies on the onlyWire setting in codegen, error checking, etc. This is a mess.