Set lineHeightMultiple when creating NSParagraphStyle from DTCoreTextParagraphStyle

- the lineHeightMultiple value wasn't getting passed to NSParagraphStyle, so set it
Add a unit test for passing of lineHeightMultiple value

- Added a test that sets a non-default value to a DTCoreTextParagraphStyle's lineHeightMultiple and checks the value of a generated NSParagraphStyle for the same value
Merge pull request #770 from adamschlag/develop

Set lineHeightMultiple when creating NSParagraphStyle from DTCoreTextPar...