nl.pelagic.util: FilenameFilterWithRegex revert C case changes

Signed-off-by: Ferry Huberts <ferry.huberts@pelagic.nl>
nl.pelagic.util: FilenameFilterWithRegex improve D case changes

Signed-off-by: Ferry Huberts <ferry.huberts@pelagic.nl>
nl.pelagic.util: FilenameFilterWithRegex update A and B comments

Signed-off-by: Ferry Huberts <ferry.huberts@pelagic.nl>