Modified `SokkiaDt500Theodolite` class to swap angles returned by
`readAngles`. This seems inconsistent with the description on page 23 of
the DT500 Operator's Manual of how the instrument provides angles, but
the angles are swapped in the data the HMMC is collecting and the rest
of the Maka code that deals with theodolite angles seems fine. Will try
to talk on the phone with HMMC folks so we can see what strings the
DT500 is returning when asked to read angles and if they're really not
what the documentation describes.

Also added "Swap Angles" edit operation to `MainWindow` class so files
with swapped angles can be corrected.