Consistent string-case treatment for input

[zooks97]

Currently, the OpenMX input schema uses the same string-case conventions as OpenMX, as written in Input_std.c (the OpenMX input parser source code).

However, it is fairly inconsistent, and importantly, the input parser is actually case-insensitive.

It could be far simpler for users if we also dealt with this case-insensitively:

• Make all top-level keywords UPPERCASE in the schema, and convert them to that after input in the OpenmxCalculation
• Make all parameters and nested keys in the schema lowercase, and convert them to that after input in the OpenmxCalculation