Verify that adding objects to standalone arrays works from Swift
Make the documented style for defining RLMArray properties on Swift objects work

Initialize the backing array for standalone arrays created with
initWithObjectClassName:, and switch the subclasses to using
initViewWithObjectClassName to avoid having them create a pointless
backing array.

Closes #746.
Remove the pointless _readOnly ivar
Merge pull request #751 from realm/tg-swift-backing-array

Initialize array properties on standalone Swift RLMObject subclasses