Feature/onetomanysupport

This pull request adds support for `ToMany` properties. 

A new example project is included.

Functionality is modelled after the Contacts app, which allows you to add multiple phone numbers and addresses for a single contact.

At a high level, this pull request adds the following public API options:
* `FXFormFieldTemplate` property with possible values `FXFormFieldTemplateToMany`, `FXFormFieldTemplateToManyOption` or `FXFormFieldTemplateToManyAdd`
* FXFormFieldClassInCollection property to specify the type of objects stored in a collection.

In the private implementation, a new `FXOneToManyForm` is added. This class functions much like `FXOptionsForm` in that it takes a field with multiple values and handles their display.