topcat: fix bug reversing cube/sphere navigation help buttons
topcat: fix CDS X-Match MOC downloads to use table ID not alias

Thomas Boch (CDS) requests that MOC downloads should use VizieR table ID
not the X-Match alias (though either seems to work at time of writing).
This means we have to wait for the metadata to be downloaded.  Rearrange
the scheduling of the relevant downloads accordingly.
ttools: fix upload matcher to cope with empty input tables

The CDS upload service currently fails with an error, at least under
some circumstances (selection=all) if there are no rows in the input
table.  So add logic which is able, configurably, to fail the match
with a well-behaved IOException in the case of zero input rows rather
than attempt the match.

Once the CDS service copes with empty upload tables this should
perhaps be switched back, since an empty output table may be of
some use (at least you can get the columns).  Or maybe not, you
probably don't want to keep the result.
ttools: add HEALPix presorting to CDS upload skymatch

Sorting the rows of an uploaded table by HEALPix pixel index for a
multi-block upload match job should in theory improve performance.
Add a parameter presort to the cdsskymatch task to turn this on.
There are some disadvantages though, so set it false by default.

It also makes it harder to do progress monitoring, so for now do
not provide this option in topcat.  For the topact xmatch progress
bar to work with this option would require (I think) a new optional
method getRowCount on ConeQuerySequenceFactory.
ttools: improve documentation for CDS table selection

Following advice from Thomas Boch, point to the TAPVizieR web page
as a way to find VizieR table (as opposed to catalogue) IDs.
Thomas admits there is no very easy way for users to do this,
may be fixed at CDS one day.
topcat: fix CDS upload window to require table metadata

Now the Go button in this window is only enabled (and coverage
information displayed) when table metadata has been successfully
downloaded for the selected table.
Thomas Boch advises this is a reliable indicator of whether the
table can be successfully matched.
topcat: fix TAP load window to stay open by default

All table load dialogues by default are disposed when a table is loaded,
but you can change this behaviour with the "Stay Open" option.
For TAP it's usually pretty annoying for it to keep closing, so set
it pinned open by default.  Maybe I should do this for some other
load dialogues too?
topcat: fix TAP load dialogue so it can be loaded early

The TAP constructor referenced the ControlWindow instance.
Moved that requirement to a later-invoked method so that the
dialogue could be invoked from the ControlWindow constructor.
topcat: replace concatenate button in main toolbar with TAP

Concatenation is boring.  TAP is more powerful than you can possibly
imagine.  It deserves its place on the main toolbar.
ttools: increase default xmatch blocksize from 10k to 50k rows

Thomas Boch says it's OK.  Also improve documentation of this value.
ttools: rename cdsskymatch parameter sr->radius

Units are different from coneskymatch sr parameter, so it's a good idea
to have different names.  Also clarify units (arcsec) in usage message.
table: STIL to v3.0-6
ttools: prepare for release v2.5-3
topcat: prepare for release 4.2