Add FormatTools methods for creating OME-XML primitive types

These methods also handle the logging of invalid values for the given
primitive type.
Update readers to use methods introduced in 55a7db

This consolidates primitive type construction and logging, so that each reader
doesn't have to worry about it.
Remove unnecessary primitive class imports
BaseZeissReader: consolidate a few more primitive type warnings
Leica: fix typo in primitive type creation
Check for null before passing primitive values to MetadataStore
Merge pull request #537 from melissalinkert/primitive-warnings

Consolidate OME-XML primitive type logging