Added form annotation builder factory

Two outstanding items for this pull request:

1. What is the best method to get it into the default service locator config?
2. Should the factory support adding custom annotations and annotation listeners to the builder?
I'd prefer to just have the FQCN here. Some advantages

 - less keys to remember
 - can be statically referenced via PHP 5.5's `ClassName::class` syntax, allowing IDE static introspection to find non-existing classes
 - less documentation required
 - more predictable from a consumer perspective