Finished convolve function

Function convolves a double image about the center of a kernel with odd dimensions. Throws an exception when the kernel dimensions are even (a single center point is required)
Updated HOG to use my own convolution function

Removed opencv filter2D and replaced with CenterConvolve as it is a project requirement to compute convolutions ourselves (I think)
Removed wait for keypress

Removed cin.get() from the test program so that it exits immediatly instead of waiting for a keypress
Changed loops to process rows before columns

Reduces the amount of cross-page memory copies to slightly speed up loops. Also simplified the first loop it was ugly.