Add ability to calculate flux for all scans, not just those in which a plume is identified

[christophkern]

In the Post Calculate Flux dialog, the menu entry "Calculate -> Flux for all scans which see the plume" allows users to calculate a flux for those scans in which a plume was identified. Working with data collected from Rincon de la Vieja, we are running into cases where the plume is likely overhead, but the instrument is detecting only minimal gas because the emission rate is too low. However, we know the plume should be overhead, e.g. because it is identified in the previous or next scans. In such cases, it would be useful to run the flux analysis on all scans, not just on the ones in which the plume was identified. The user can then choose which scans they believe. The scans in which the plume was not identified are clearly visible in the PostFluxLog because the scan angle is set to -999 and the plume completeness is set to -999.
If possible, please add a menu entry "Calculate -> Flux for all scans".