ttools: add optional histogram weighting coordinate
topcat: update jar file manifest attributes

Versions of WebStart after java 1.7.0_51+(?) under at least some
circumstances require the "Permissions" attribute in the signed
jar file manifest
(https://blogs.oracle.com/java-platform-group/entry/new_security_requirements_for_rias).
This is now present in the jsamp.jar file (signed or not).
topcat: rename legend control positioning tab

Use the name "Location" not "Position" so that it doesn't clash with
the plot coordinate tab.  A name clash is slightly annoying because the
selected tab persists based on tab name.
fits: improve nullable integer logic

Avoid a pre-processing pass to check whether there are nullable integers
in each column if all such columns are declared with all the metadata they
need in relation to nullability (i.e. a blank value).
In this way, by declaring a blank value for nullable columns you can
avoid a first pass for FITS output.
topcat: allow more control from PlotTypeGui

The gang layer manager will look at the order of the given plotters
and pick the first one as the default layer control.
topcat: add plot2 window specifically for histograms

You can already plot histograms in the plane plot, but having a separate
window can set up some defaults in a more convenient way if a histogram
is what you want to plot.
topcat: customise histogram axis control

It now has a "Bars" tab which allows global control over the bin size,
normalisation status etc.  Reranging takes place when these attributes
are changed in relevant ways.
topcat: histogram has a Bars control alongside Axes control

Refactored so that the AxisControl class is replaced by an AxisController
class that owns one or more Controls.  This allows the histogram plot
to control a Bars control alongside the Axes control.  That looks easier
to understand in the GUI.  For now, all the other AxisController
concrete subclasses only have a single control.