Merge pull request #200 from anizami/image-tests

Adding image unit tests
updated aplpy,axis labels, tick labels, grid, colorbar and frame
added slicer, made formatting edits in other files
edited ticks and wcs_util
minor changes of _ax1 to ax
various bug fixes
only one test with formatting scalar coordinates with % fails now
removed contour_util file, also noticed contour test failures
removed WCS class
using wcsaxes to show markers, circles etc  now
temporarily fixed showing contours
the cursor_world code works now, show_colorscale also magically works
checking inconsistent format works now
worked on some todos, bug fixse
reverting back to wcs_util.WCS, adding and removing grid works now
removed set_xlim and ylim in show_contour
removed wcs_utl WCS again and implemented setting plain or colons formats
draws minor ticks now
refactored code to set x and y spacing for ticks
removed commented out WCS class, changed pixelworldmarkers tests