Link shared library to opencv libraries

Linking libraspicamcv.so against opencv_core and opencv_highgui allows the SO to be loaded in python using ctypes.
Otherwise, the cvResize function will not be recognized. Sample python code:

#############################
from ctypes import *
cdll.LoadLibrary("./libraspicamcv.so")
libraspicam = CDLL("./libraspicamcv.so")
#############################