New camera viewfinder settings API.

New camera viewfinder settings API.

There already was a control interface for the viewfinder settings
but no real public C++ API and a partial QML API.

This patch adds a new C++ API and improves the QML API.

Supported viewfinder settings are resolution, minimumFrameRate,
maximumFrameRate and pixelFormat. The camera can be queried for
the supported values for each of these settings.

A new control interface was created to match the new API.

Change-Id: I289fea038fe46277a5516c956a64280da09ed985
Reviewed-by: Andrew den Exter <andrew.den.exter@qinetic.com.au>