Add support for LSynth parts

Partly fixes #75. Tested with example model @virtualrepublic sent in #75 and works as it expected (at least, it seems as if it does).

@virtualrepublic Would you please test this and make sure it works? I'm still working on the `UnicodeDecodeError` (see #76 for details). For now just remove that character from the file (https://github.com/le717/LDR-Importer/issues/75#issuecomment-43395324) to overcome the error. :wink:

@rioforce Will you checking the GUI text and make sure it is good?