Added new ENABLE_XXX_FILTERING keys, code factorization in 1dinterpolations and new option for decimal dates in CSV plugin

It seems virtually impossible to collect all <section> tags from the XML
to re-build here without recreating the better part of the recursion
process, in effect doubling Inishell's core.
Hence, it is now a restriction that dynamic INI sections must go in a
dedicated <section> tag (as has always been supported) and can not be
scattered accross multiple stand-alone elements.

Height and width set in XML have just been ignored (they were expected
as option nodes, not attributes).
This has been fixed. Please revisit your spacer sizes...

Some missing keys in the katabatic flows module have been added, some
unnecessary keys removed from MeteoIO (no need for POIs there). Some
file extensions are now specified as filters when it makes sense.

The spatial_resampling, 1d interpolaitons and 2d interpolations have
been renamed to have more consistent naming.

This is necesary for the packaging (it is much beter to have an
"inishell-apps" folder in /usr/share than an "applications" folder)

It is not perfect in the sense that the 2DInterpolation section must be created anyway, independently of the use of spatial resampling or not. The same applies to the Grids2D configuration frame. A message is shown to the user, explaining when these should be used...

Alternative way of presenting the data creators (save space in crowded section, uniform with MeteoIO doc)

Now the meteoio_plugins and meteoio_gridplugins files are not needed anymore, they have been replaced by more modular files. The new syntax for the WINSTRAL spatial interpolation has been implemented. A buggy input field in Snowpack has been fixed (NUMBER_OF_SOLUTES).

The XML files had inconsistent case for the section names, this has been fixed. A mis-indenting has been fixed in help_dev.xml

But still lots more to do!

Thanks to the includes, we are now much more granular. But more work is needed with better handling of defaults, more thoughts about colors and making sure all MeteoIO and Snowpack keys are represented.

Disable panels' context menus for grouping elements that could show up on a few pixels. Minor XML tweaks and (very) minor code optimization.

Don't auto-select items in editable dropdown, give key as tooltip if no help available, minor MeteoIO XML changes

Fix reading a decimal number with more decimals than previously (it was only checked, not set to the widget). Add some MeteoIO XML.

Modify default checkbox labelling behavior: if a caption is given but no label - hide the label instead of displaying the key (most common use case). Some more XML

Fix doubled elements because of faulty XML references parsing with nested include files _and_ references. A little bit of the new meteoio.xml and some file cleanup for it

simulation. This is work in progress of course, but there's already a lot of information for
the interested user, and it should be more than enough for people knowing
INIshell v1. A few minor tweaks along the way.

then it's handled by them. No more duplicate missing keys in this case
either.