Continuum maps

With the new correlator system, it is better to create continuum tables from the ``line'' backend, using command
SET SELECTION CONTINUUM DSB L01 TO L06
for example. When line contamination is possible, the best way is to build the UV table in pieces, as for example in the following command procedure:

FIND
SET SELECTION CONTINUUM USB L01 TO L04
TABLE CONT NEW
SET SELECTION CONTINUUM LSB L01 TO L02
TABLE
SET SELECTION CONTINUUM LSB L04 TO L06
TABLE

which creates a continuum table for data contaminated in subbands L05 L06 in upper sideband, and subband L03 in lower sideband.