Do not normalize field names to UPPER Case

[mattywausb]

When working in context with Json, the correct upper lower case of field names is relevant to shorten the declaration.
So the dvpi must preserve the original writing of a field name.
Until then, we need to declare json_path for all fields.

Additionally the declaration of a stage_column_name must be possible to allow parallel field names with different cases. Stage column name and column name default to upper of field name.
A check to detect duplicate stage column names must be implemented

The dev sheet render must check, if there is any kind of json specific processing declared, and add this to the sheet output accordingly.

• dvpd syntax reference extended
• dvpi syntax reference extended
• test cases added
• dvpdc modified
• mod dev sheet modified