wld: Change treatment of "kloeketoelichting"

[ErwinKomen]

The treatment of the 'kloeketoelichting' needs to change. Meaning: [kloeketoelichting] represents an additional comment on a [dialectopgave] (Entry), meant for a specific location ('dialect').

Note: each "Entry" is already specific for one location/dialect.

Implementation:

• Add field 'kloeketoelichting' to model "Entry"
• Remove field 'toelichting' from model "Dialect"
• Change the processing of 'kloeketoelichting' in models.py::csv_import() accordingly
• Re-read the data
• Visualisation changes: a) Only show 1 (one) Entry.toelichting where it doesn't change between dialects b) Show the Entry.kloeketoelichting after its dialect-mention

[ErwinKomen]

I have made the necessary changes for the e-WBD to implement this. TODO: implement these changes for the e-WLD too.