Replace '_' with space in field name.

When translation and fallback not available, it uses field name for translated text. I changed it to replace '_' with space so that 'customer_name' field will be translated to 'Customer name' without having to define in language file.
Adjust mockTranslator to cater for HelpersTest.testTranslateFieldNameUnderScoreToSpace
Added new test for replacing '_' to space in field name
Merge pull request #199 from gazard7/patch-2

Replace '_' with space in field name when translate