Empty vs. null database fields and cleanup

[ahankinson]

A number of fields in the database have a significant number of empty string values when they should be null. Here's a few of them:

main_app_chant.manuscript_full_text
main_app_chant.image_link
main_app_chant.indexing_notes
main_app_chant.volpiano
main_app_chant.volpiano_notes
main_app_chant.volpiano_intervals
main_app_source.description
main_app_source.selected_bibliography
main_app_source.summary

That's not an exhaustive list.

In addition, a number of text fields start with a space or carriage return, and those should probably be stripped since they will cause problems with sorting. Particularly the 'manuscript_full_text' and 'manuscript_full_text_std_spelling' columns.