Refactored Heat API configuration

- All settings moved to tuskar.conf
Return the Heat stack in JSON on DataCenter#index
Fix regression with ResourceClass/Flavor from recent rebase hell
Merge pull request #61 from marios/fix_resource_class_flavor_regression

Fix regression with ResourceClass/Flavor from recent rebase hell
Merge pull request #56 from mfojtik/heat_conf

Heat API configuration refactoring