Creating /v2/apps will create a parent /v3/apps

[#79386466]
Deleting a space deletes the v3 apps associated to it

[#79386466]
Added "/v3/processes" resource endpoint.

 - Validate that process receives an app_guid on creation.

[#79386466]
Prevent deletion of apps that have child processes

[#79386466]
Bump vendor/errors

 - Adds 409 Conflict

[#79386466]
Prevent deletion of spaces with a v3 app associated to it without recursive=true

[#79386466]
Add POST /v3/apps/:guid/processes to add processes to app

 - Refactor ProcessesController to call to ProcessesHandler, which is
 responsible for dealing with request bodies and raising the appropriate
 API errors when necessary.
 - Reuse ProcessesHandler on /v3/apps/:guid/processes

[#79386466]