Show x and y offsets outside system tabbed panel

THK requested the ability to set position offsets for systems other
than spherSystem.  It looks like the OT actually remembers the
offsets from the spherSystem and writes them into the XML when
using other systems anyway.  This commit makes the offsets panel
visible at all times (for UKIRT) by moving it outside the tabbed
panel.
Trap IllegalArgumentException filling target table

RADecMath.string2Degrees throws IllegalArgumentException when
given a coordinate system other than FK4 or FK5.  This causes
a problem filling the table, which in turn prevents successful
changing of the target type.  For now trap the error and display
"ERROR" in the table.