Entity overhaul

[bmcclure]

This PR is huge in scope, but it's hard to split up further because a lot of things within Launchpad are built on top of the entity system, and also built with the classes that the entity system is also built with.

These changes serve several purposes, mainly:

• Allow all entity types and entities to be defined by modules
• Allow entity types to be defined using generic, reusable classes
• Separate the concepts around entity lifecycles to services and service factories
• Make entities fieldable with generic definitions which can be modified and extended
• Make entity forms automatically build using field widgets and field definitions

A lot of concepts in Launchpad have to be rethought during this process to make them more generic as well.

The end result should be that most of the functionality can be moved into modules so that the core is more lightweight for users who don't need everything. Additionally, users should be able to install third party modules which can extend the entity system in any way they see fit.

[bmcclure]

At this time there are several things broken that need to be fixed before this branch is merged:

• Field value changes not persisting to config files
• "Simple" launcher editor UI is partially broken
• Some entity values aren't rendering properly on entity forms or storing properly in the entity data
• Backup and Platform entities need testing and additional work most likely
• The Launcher Wizard needs to be replaced with a "create" entity form
• Starting and stopping extra processes during game launching is being rebuilt and is currently broken

[bmcclure]

The entity overhaul is complete, though there are likely to be some significant hitches before it's stable enough for a full release.