pco: add global shutter support
pco: add "global-shutter" property
Minor reformatting in pylon plugin build script
Update pylon-plugin to libpyloncam 0.4
Improve robustness of roi setting for pylon plugin
Implement auto exposure property for pylon plugin

Conflicts:
	plugins/pylon/CMakeLists.txt
	plugins/pylon/changelog.txt
	plugins/pylon/uca-pylon-camera.c
Add missing property specification for exposure-auto
Fix printing non-existent error

This caused a segfault when unreffing a camera object which was still recording
but stopping it was not failing.
Add Python support code to release GIL on grab

A compile time switch WITH_PYTHON_MULTITHREADING has been added that toggles GIL
releasing.
Release version 1.6.1