Issue #1033: Add API to get/set Emulate Brush Dynamics

This is a revival of @Massimo's patch to resolve issue #1033 (closed).

It adds an API to get and set the Emulate Brush Dynamics property of the Stroke Paths dialogue in scripts and plug-ins. Per @Jehan in #1033 (comment 216548), this is most likely good since it just sets and gets a boolean value. 😄

Since we're finalizing the API, I thought it'd be nice to finally include this rather than leave the patch stuck in an issue report. This patch does add new strings, but like most of the PDB API it's not marked for translation so it shouldn't impact the string freeze.

@pixelmixer Hi! If you have the time, I'm curious if this API would be a useful addition.