ttools: added more overloads of Conversions.toString function.

toString was failing to resolve for byte and boolean types.
Add two more overloaded versions so that it's always(?) OK to write
"toString(expr)" and get a result.
topcat: add new Highlight Rows action.

When a new subset is created, its rows are selected in the table viewer
window and it is made visible in all plots.  However, as pointed out
by Karl Glazebrook, there is no easy way to force this action for an
existing subset.  Added an action to do this in the Subsets window,
and a similar action in the table viewer window which just highlights the
rows without affecting plots.  Also withdrew the (slightly dangerous,
undocumented, and iconless) Apply Subset action in the table viewer window.
ttools: spectrogram improvements.

Ensure pixels are plotted even for very thin time extents, and
provide external information about coordinate order.
topcat: generalise ColumnDataComboBoxModel.

You can now provide custom conditions for what column types are
acceptable, doesn't have to be just a class that content type
is descended from.
cdf: update JCDF library to v1.0
table: Add DomainMapper.

A domain mapper allows the possibility to associate conversion behaviour
with a ValueInfo (e.g. a column).  It's necessary to have something like
this in order for the CDF table reader to be able to communicate information
downstream about how to make sense of various CDF-specific time encodings
(CDF_EPOCH, CDF_EPOCH16, CDF_TIME_TT2000).

This is a change to the ValueInfo interface, i.e. the core of STIL.
Since ValueInfo is mostly used via the DefaultValueInfo implementation
however, the change is not likely to require source code changes
to client code.
topcat: Display domain mapper in column info window.
table: Add DomainMapper instance for Time.
table: ASCII-like tables now use Time domain for ISO-8601.

CSV, IPAC, ASCII (and other?) tables now insert an Time DomainMapper
into column metadata when they can identify ISO-8601 dates in a string
column, so that such columns can be correctly treated in the time
domain by downstream processing.
votable: VOTables now report Time domain for ISO-8601.
cdf: CDFs now report Time domain for epoch-like columns.
ttools: plot2 DataSpec now reports column metadata.

The new method DataSpec.getUserCoordInfos means that the plotting system
can acquire column metadata rather than just values for plotted columns.
This in turn will make it possible for plots to acquire a DomainMapper
to make sense of domain-bound column values.
ttools: plot2 Coord now uses value domains.

The Coord objects that specify where plots get their data from are
now capable of specifying their required data domain,
and using mappers supplied in response to convert values from
some potentially non-obvious input form to a usable common value domain.
table: Remove JTable presentation items from ValueInfo.

ValueInfo used to contain getTableCellRenderer, and DefaultValueInfo
had getTableCellEditor as well.  These really didn't belong there
and as far as I know were not used outside the table package, so
move that into uk.ac.starlink.table.gui(.StarTableColumn) where
they are happier.  I may provide another interface later for tables
that want to provide customised JTable GUI options.

This is a change to a class that's fundamenatal to the STIL API -
but probably not a big deal even so because I doubt anybody used
these methods.