Xy box fix

[christinawlindberg]

Fixed xy vs ra/dec priority ordering for checking whether a source density tile is within the boundary area or not. This is a short-term fix for Issue #704. Long term we will need to either figure out if shapely allows diagonal boxes or to just phase out xy functionality completely (although I'm personally not in favor of this plan)

[codecov-io]

Codecov Report

Merging #706 (2e745cd) into master (c07b3ad) will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##           master     #706   +/-   ##
=======================================
  Coverage   43.83%   43.83%           
=======================================
  Files         100      100           
  Lines        9730     9730           
=======================================
  Hits         4265     4265           
  Misses       5465     5465           

Impacted Files	Coverage Δ
beast/observationmodel/ast/make_ast_xy_list.py	5.04% <0.00%> (ø)
beast/plotting/plot_ast_diagnostics.py	9.09% <0.00%> (ø)

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[cmurray-astro]

LGTM! definitely open an issue re keeping the xy region capability around long term