Convert and/or filter onchange functions in block generators

[MatzElectronics]

A number of blocks use onchange handlers - and even the simplest projects fire those off like crazy in blockly, so that code is running near constantly.

Each onchange should either:

• be replaced with a function that is explicitly called
• use a conditional and only run the remainder of the handler if the event triggering it applies

This should have the effect of speeding up blockly (preventing it from lagging)