preserve original offset when parsing SM files

[jhaco]

Current:

• When parsing data from an SM file, the tool bakes in offset time into the rest of the note data. This was needed to work with StepCOVNet, since it doesn't consider offset timings using current methods.
• When parsing an SM file, and rewriting back to a different SM file, it's highly possible that the note colors have changed due to them being placed differently with the offset baked in.

Path Forward:

• Could be tricky, but I could probably add in a flag to not bake in offset time and preserve original data while extracting note timings. Depends on whether this is needed with how current convolution methods only consider timings...