Added the ability consider whether the the user exlicitly specified the label or the framework generated it when applying global custom formatting.
Cache the test for parameters size of label_text for better performance.
Changed call to label_text to always pass the new thrid parameter, and made the default a proc that ignores it. This is a breaking change.
Merge pull request #786 from timscott/master

Consider whether the user explicitly specifies a label when applying global custom formatting

Conflicts:
	lib/simple_form/components/labels.rb
	test/form_builder/label_test.rb
Use lambda to document we accept three arguments
Add CHANGELOG entry for #786