Major revision to transcription script.

1) Most of the code is now encapsulated in procedures. For example, transcription of each segment is handled by @transcribe_segment(...) which in turn delegates to @transcribe_vowel(...) or @transcribe_consonant(...).

2) CV trial type has been generalized so VC and CV trials are now supported.

3) Start-up wizard now re-uses code from segmentation start-up.

4) Minimum version of praat is now enforced. Praat commands that uses "Command... ['rgs]" notation have been replaced with the recent "Command: [args]" notation.

5) Procedures are also used to contain or (hide) related variables in a common namespace. For example, @nwr_trans_textgrid defines all the variables needed to define and describe the transcription textgrid -- for example, its filepath (nwr_trans_textgrid.filepath$).

6) Multistep transcription wizards (consonants, prosody) support a back-button.

7) Functionality is now broken up over multiple files.
diphthongs now scored for frontness and backness based on the first vowel in the diphthong. /l/ and /r/ added a "voiced" "alveolar" "glides".
update prosody scoring to -1 for inserting segments and -1 for deleting segments. the textgrid also records whether a vowel was inserted