ENH: respond to end batch process events to update widget

When a markups file is loaded, the node added event is ignored
because the scene is in batch process mode. Connect and respond
to the end batch process event so that when a markups file
is loaded and it's the first markup in the scene, it will be
set active and shown in the GUI. If the scene contains an
active markup node already, the newly loaded one will not
be set active, it has to be selected from the drop down
menu.

STYLE: removed trailing spaces.
STYLE: give user a hint about jump to slices

Added to the tool tip that you can click on the table's
name column to jump the slices to that point location.
BUG: prevent MRML updates to the table from updating MRML

Blocking signals is a brute force solution, but it's preventing
the seed widget from getting further and further from the mouse
as a fiducial is dragged. In updateRow updating the cells with
the fiducial location was triggering a cell changed signal
even with checking that the number value as a text string
had changed.
BUG: fix jumping of all fiducials to the slice where one fid was

The widget call backs for 2d and 3d fiducial displayable managers had
the same class name and was causing a conflict and resetting of
mrml coordinates.
There was also a logic bug that was calling UpdateNthMarkupPosition
when the seed widget position changed, but that was updating
the seed position. Renamed that method to UpdateNthSeedPositionFromMRML
to be very clear about what it does, added UpdateNthMarkupPositionFromWidget
and call it from the call back.
Updated the check on if positions changed when updating all the points
to be more logically clear. TODO: check if need the disable modified
and explicit invokation of point location modified/markups modified.