Added overridable editorClass and editorAttrs to Form.Editor

Bootstrap 3 now requires a `form-control` class on form elements. Unfortunately the `editorClass` and `editorAttrs` were not globally overridable like `Form.template` was making templates overrides for Bootstrap 3 a pain in the butt.

This pull request adds the `editorClass` and `editorAttrs` to the `Form.Editor` properties and allows overriding in the following (going from most precedence to least): Schema Definition > Individual Editor Class > Base Editor Class.

NOTE: `schema.editorClass || this.constructor.editorClass || Form.Editor.editorClass` has to be 3 parts as the class properties from `Form.Editor` are cloned and changes will not propagate. We need the 3rd check to look to the parent. This gives us the benefit of allowing us to globally override all Text editor classes without affecting other editors.