Unify settings for solution and project setups.

Create a single solution platform named x86.
Ensure both Debug and Release configs build to the root for all projects.
Ensure all Release configs generate pdbs.
Deduplicate OpenRA.ico.

Use a path with backslashes to satisfy VS2012.
Merge pull request #5403 from RoosterDragon/solution-config

Unify settings for solution and project setups.