Switch libs to SDL2 snapshot (2.0.0-6940).
Import SDL2 includes from 2.0.0-6940.
Rename "sdl" build dir to "sdl2".
Link against SDL2 (Win32).
Port to SDL2.
Upgrade SDL2 snapshot to 2.0.0-7024.
Provide access to the window and renderer.
Port to SDL2.
Update custom build steps to install SDL2 DLLs.
Exclude OIS-SDL bridge on Win32.

We don't use the bridge on Win32, and we'll probably be replacing OIS
with the built-in input support from SDL2.
Port to SDL2.
Promote layout flags enum out of UiViewModel.

This greatly simplifies usage and allows it to be used in both Display
and UiViewModel without a circular dependency.
Refactor UI-space conversion to Display.

This allows views to convert from UI-space to screen-space coords even
if they don't use SdlDisplay::DrawUiTexture().
Port to SDL2.
Use SDL2main.
Port to SDL2.
Convert the OIS init exception to Exception.
Abort when the window handle could not be found.
Properly initialize SysWMinfo.
Remove explicit window placement.

SDL handles placing the window at the correct initial location, so we
don't need to move it ourselves.