#670 Reduce number of files in CB PCH common file sdk_common.h

[Tim Stahlhut]

This patch reduces the number of CB headers included in sdk_common.h.
The reason is to reduce the number of times where the CB PCH files need rebuilt.
The inclued kept were based on the number of the times there were included.
But, the including of "cbplugin.h" and "wx/wxscintilla.h" were removed because they change to often to be in an Precompiled-Header (PCH).

Tim S.