Extend constructor instead of initialize for base classes

See #281 and #294.

Override `constructor` of `BaseModel`, `BaseCollection`, `BaseView`,
`BaseApp` instead of `initialize`. Add a deprecation warning to
`postInitialize` in `BaseApp` and `BaseView`.

This should have zero behavioral changes.
Merge pull request #320 from airbnb/nuke-postinitialize

Extend constructor instead of initialize for base classes
Trivial removal of unused variable layoutPath.
Merge pull request #322 from chug2k/master

Trivial removal of unused variable layoutPath.
store instances of models or collections

instead of their serialized data.

The store doesn’t create new instances anymore which fixes problems with
event bindings.
Merge remote-tracking branch 'origin/store-instances-instead-of-data' into mergedMultipleFixesFor1UP