[ALOY-747] Alloy: Add attributes to override create, add and remove methods

This issue builds forth on TC-2609, asking for dynamic namespace loading for Alloy view components. If using existing object factories, being either native or CommonJS modules, these might not always follow the convention of createTagName, add and remove for creating the view component, adding a child to it or removing it. Using optional toCreate, toAdd, toRemove attributes, one should be able to override these defaults, so that:

<Alloy>
  <MyView ns="my.factory" toCreate="get" toAdd="attach">
    <Label>Some label</Label>
  </MyView>
</Alloy>

properly translates into:

if (typeof MyFactory === 'undefined') var MyFactory = require('my.factory');
$.__views.__alloyId1 = MyFactory.get({ .. });
$.__views.__alloyId2 = Ti.UI.createLabel({ text: 'Some label, .. });
$.__views.__alloyId1.attach($.__views.__alloyId2);