Convert from using Entity Registration to using Ticket module

One of the largest issues we've had with COD 7.x is registration. Unfortunately, registration was built for a narrow use case that doesn't easily fit how COD is meant to be used.

After consulting with the maintainers of entity registration, jyee and japerry have taken on re-writing it in a new module called 'ticket'. Many constructs of entity registration are still there, but the architecture is fundamentally different.

Ticket architecture entities:
Ticket type, Ticket Registration, Ticket state (optional)

Ticket Types
These entities describe the type of ticket an event may have. It shows the availability, min/max per order, product, etc. Each product type is defined per event via a product type field. The difference between this and Entity registration is that these settings are part of the entity instead of the field definition. This allows us to make different ticket types per event, which is currently restricted to one with registration module.

Ticket Registration
These are the entities that have definable fields the implement ticket types (first, last, address, etc). Since we have ticket types acting as bundles of ticket registrations, we can create different fields for each type of registration, while still containing the global settings under the ticket types entity.

Ticket State
This is essentially registration state. Much of the code was re-used from Registration state, since its doing the same thing. Its only responsibility is to assign a state for a registration. Ticket types can define the default ticket state that a registration starts with, and other modules can modify them. For instance, in COD we have 'Complete' as a default state for free events, but paid events would alter the default state to say Pending.

Most of the ticket module has been complete, and we will be using this issue to track progress of its inclusion to COD. If anyone wants to write a migration/upgrade path from one to the other, that'd be awesome!