Visualize the search line and/or PIV search window on the Image Velocimetry Tabs

In the Image velocimetry tabs:

1. Plot the gird nodes where velocities will be computed, using the points in the Grid Preparation AnnotationView
2. Plot some visualization of the search line length on the Image Velocimetry tab
   • STIV: This would be a line of the length n_p in the directions of \phi_o
   • STIV Optimized: Plot a circle with a radius of n_p around each point. Symbolize in some way that is simple to see (e.g., no fill, thin white dashed line border). This will require a modification of the Circle class in graphics.py -- or perhaps a new class based on PolygonAnnotation.