Changed package origin to current project location

Updated contact address and GST_PACKAGE_ORIGIN to point to https://github.com/TheImagingSource/tiscamera
Added basic auto focus implementation

The gstreamer module allows the user to simply activate the focus
functionality for the whole image, or to select an image piece that
shall be focused.
Added gst_autofocus to build system

Will only be built if aravis is used.
Cleanup in configure.ac