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

renamed the undst filter into shift, removed time restrictions on the time filters (as this is not applicable)

And some mandatory parameters that were not tagged as such have been
properly marked as mandatory

As well as some reformatting for some help texts

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

And fixed an inconsistent option (between SUPPR on single parameters and
on time).

When both a default value and precision=... where provided in the xml
file, the precision was reset to the default precision. Now the default
precision is reset to the XML provided precision.

In order to give the user the required flexibility to enter the numeric
values he/she wants to, precision specifications have been almost
everywhere in the xml files (a few places still rely on the default
settings because it makes sense). The units have also been added where
possible.

For the Kalman filter this is not possible yet because of changes
requiring anything entered in a Number's expression to be a complete
formula.

Implement mechanism to translate custom syntax to tinyexpr before styling (so e. g. hardcoded substitutions are allowed exactly like in some filters)

This fixes issue 829 with MeteoIO's "*::EXCLUDE" kind of keys. Moreover,
the new option for MeteoIO's deGrass filter has been included in the xml
file.

Of course, this means that "performant=true" must be replaced by
"pre-generate=false" for the same behavior.

Some filters had unnecessary constraints that have been removed. Some periods in seconds were expressed as a number and have been replaced by an expression for clarity.

'Alternative' panels. Better error messages.

Now for nodes where we know that the performance saving workaround
makes sense, we can explicitly set it in the attributes. By default,
all children are built. Result: E. g. GEO_HEAT will be filled correctly
even if it's not used because SNP_SOIL is FALSE (without having to state
that it should work in the XML).

Moreover, one color used in meteoIO_filters has been tweaked to be more visible in dark theme

Fix two subtle bugs where a wrong error would be displayed and in some situations the help could not be loaded via keyboard shortcut

They were left over from testing out GUI elements and may have been the
oldest untouched INIshell code... now they are cleaner and less
intrusive.

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.

Improve SNOWPACK stability corrections documentation, and a try to make a setup with very many filters more readable.

Another hotfix for propagating Replicator numbers... now, replace only the first occurrence of '#' so keys like 'TA::FILTER#::ARG#' work