Added initial asset management structure.

Summary:
This adds the initial structure for the asset management tool.  During this I've identified two issues:

* Existing UI frameworks aren't going to work for this (they're all pretty much XNA specific, or they suck), so we need to write our own.
* We can't actually run two XNA games in the same process, so the asset manager will have to communicate over the network to the game.  We can probably do this via Dx.

Test Plan: Run `Tychaia.exe` with the `--asset-manager` parameter (you'll need to do this from the command line, make sure you cd into `Tychaia\bin\Debug` first).  It should start the asset manager.  When you close or exit Tychaia, the asset manager should also close.

Reviewers: Sabre070

Reviewed By: Sabre070

Maniphest Tasks: T51

Differential Revision: http://code.redpointsoftware.com.au/D50