H/W acceleration status fixes.

Hi,

I'm making this PR so we can discuss how we want to show H/W accel in the status bar.

Here are some old images https://www.dropbox.com/sh/oh3ksmpma82707a/5RPLbM3C-D
Test build: https://dl.dropboxusercontent.com/u/16282309/MPC-HC/MPC-HC.1.7.1.270.x86_dxva_status.7z

For LAV it will show `[DXVA2 Native]`, `[DXVA2 Copy-back]`, `[NVIDIA CUVID]` or `[Intel QuickSync]` depending on H/W acceleration type used. 
For other decoders it will show `[DXVA]` or `[DXVA2]`.

I'm open for suggestions :)