Adding regexString property to US2Condition base class

Adding a regex string property to the US2Condition base class
Updating all regex based US2Condition subclasses to implement new regexString
property
Users are now able to override US2Condition's regexString property if they wish to
implement a custom regex string check.
Merge branch 'master' into development

Conflicts:
	US2FormValidationFramework/source/conditions/US2ConditionEmail.m
Updating US2ConditionEmail to correct regex string
Updating podspec for version 1.1.0
Merge branch 'master' of github.com:ustwo/US2FormValidator