Create a FLAG array that tags each pixel

[MatthewWhiting]

It should be possible to have an array that tags each pixel with various ENUM values - much as we do with the new growing class.

This could be filled at the start, and be carried with the Cube class. This way you could tag pixels according to each threshold (primary & growing) and you could then just run through and pick up the "growable" ones in the growing stage.

The advantage of this is that it could then be used for the variable-threshold case in the ASKAP development. As you go through and find the signal-to-noise at each pixel, you tag the pixel according to where is SNR is. This way you don't have to go back and recalculate the SNR for the growing stage.

The flags would of course keep track of MW channels, and BLANK pixels. In fact, this could be done at the reading in stage, and would then obviate the need for the isBLANK functions throughout.