Increased default systemp value, and plot UV amplitudes to make sure that the data look 'real.'
Added ability to apply negated leakages.
Added *_snapshot() functions, which are updated versions of the original simulations; the latter are now defunct.  The new functions analyze the resulting PA and % with UVFLUX; they don't solve for GPCAL, since we're now simulating what it's like to calculate PA and % on source data with slightly modified leakages.