added Available boolean to OptionItem

related to #114

Needs more JS work from a front end dev.

If marked unavailable, adds 'class="outOfStock" to <option>.

Need JS to disable "add to cart" button if option is selected.

Also display a message - "Temporarily out of stock"
allow extension in index function
BUGFIX options array throwing error
Merge pull request #148 from nhorstmeier/BUGFIX/modifierError

BUGFIX options array throwing error
Merge pull request #142 from jirish/optionAvailable

added Available boolean to OptionItem
Merge pull request #147 from jirish/integrations

Allow extension in FoxyCart_Controller:index() function
product options processing
product options
datafeed
address cleanup