ContentRepository: Add overloads to patch update commands

[HeyJoel]

It would be handy if you could patch an update command and execute it in a single operation e.g. by calling contentRepository.MyEntity.UpdateAsync(command => command.Title = "New Title"); whereby the command is initialized with existing data and the lambda function allows you to alter any properties you want to change.

[HeyJoel]

Fixed, will be release in v0.10.

• All patchable commands in the content repository have been updated to have an overload with the new patching format
• A new method IDomainRepository.PatchCommandAsync() can be used to execute generic patchable commands

In doing this the following changes have been made:

• A new set of interfaces IPatchableCommand and IPatchableByIdCommand has been added which need to be implemented by command to indicate that it is patachable. This is really a marker interface and it just means that you've added the companion query handler to get the patchable command.
• GetUpdateCommandQuery has been renamed GetPatchableCommandQuery and moved to the Cofoundry.Domain.CQS` namespace.
• GetUpdateCommandByIdQuery has been renamed GetPatchableCommandByIdQuery and moved to the Cofoundry.Domain.CQS` namespace.