Caveat: there might be some duplicate work or lost work as we refactor
over the next year or so.

Here goes:

1) Make MosaicFT and WProjectFT gridders available to imager

2) Refactor DOimager methods so that users can pick

   a) Algorithm - Clark
                 - Hogbom
                 - CS
                 - Mscale
                 -Mem
                 -NNLS
    b) Gridder  - GridFT
                - SDGrid
                - GridBoth
                - MosaicFT
                - WProjectFT
                - WFMemoryFT (we're keeping this till memory is not a
problem for WProjectFT)


    c) MultipleField - Yes
                     - No

    d) Go back to Visibility -Yes
                             - No