Split up large test suite

... and a minor change to the Karma config (now using PhantomJS).
Added `options._externalEvent`

options._externalEvent is available when the selection in a collection is
altered during an `add` or `remove` action.
Fixed bug when instantiating SingleSelect with more than one selected model

In model-sharing mode, when creating a single-select collection, passing
multiple selected models to the constructor should have deselected all
but the last of the models. Didn't happen.
Updated build and reports