load image using ndimage.imread, use green channel

If the image is a jpg and has three channels, use the green channel (1).

If the image is a tif, assume it comes from the phantom and has bad
pixels, so fix them with a median filter.  This can be removed for new
data after camera is repaired.

	modified:   positions.py
Use convolve for center dots as well as corners

	modified:   positions.py
Update todo list

	modified:   TODO.otl
Tweaking threshargs

	modified:   positions.py
print output file save name

	modified:   positions.py
Relaxed threshargs to allow all particles

From this commit all "fast" "equilibrium" datasets were found.  Results
must be filtered beyond this, since threshargs are very loose.

	modified:   positions.py
Merge branch 'subtraction'
Some new functions and important fixes:

    orient_corr()
        returns g_m(r), now works properly

    dtheta(i,j,m)
        the proper smallest difference of two angles mod m

    local_particle_orientational()
        the average of the local phi_m, calculated for a voronoi
        cluster, averaged over all frames

    get_neighbors
        returns neighbor ids for voronoi neighbors of given particle

	modified:   correlation.py
More notebook additions:

    mostly just updates with new november data.
    fixed g4(r) and the angle histogram.

	modified:   corners.ipynb
	modified:   orientation.ipynb