The Snowpack [Input] section has been restructured like MeteoIO's in order to allow replicating such sections

The FORCE_SW_MODE key in [SnowpackAdvanced] had never been exposed in Inishell... This is now done!

The order between the "snowpack_advanced" and "tech_snow" sections has been changed in order to be more natural.

Fix deprecated folder location

See merge request !4

This would not compile in newest Qt6. Any unwanted repercussions here?
Also probably a typo in the SP help?

Fixed some datetime types and declared the new SYNTH plugin (but it is commented out as not everything is ready in MeteoIO)

it is also now possible to provide both CSV_UNITS and CSV_UNITS_OFFSET /
MULTIPLIER (see matching commit in MeteIO)

The help texts have been fully rewritten, a new type has been added "COMPONENTS"
in order to clarify what is required to parse date and time by components.
Please note that actually, MeteoIO does not use the CSV_TIMESTAMP key, it is
only there to structure the GUI.

More code replication but more features for the user...

Since default values trigger the printing of the matching keys in the
ini file, explicitely setting default values in SnowpackAdvanced
triggered the writing of a fully populated section in the user's ini
file. This is risky (the user might decide to edit some of these keys
manually) and makes it harder to spot dangerous configuration options in
an ini file. Therefore, the default values have been removed (relying on
Snowpack having them anyway) and are now only provided in the help text
(which also provides an incentive to read the help text).

The Error class was pretty much the first one to exist, and this level
indeed turned out not to be used... it doesn't even really make sense
the way everything works now.
Also cleans up a tiny bit of Qt5 compatibility

The .pro file would set this in the past. Considered switching to
"ifndef NDEUG" but that seems silly, and add_definition but this way
should be trouble-free hopefully and all the code stays the same... feel
free to switch to a more proper way!

If Inishell crashes then the log can be retrieved. This is not possible
of course for users running binaries without compiling, so if we ever
have a use case this could grow into a user setting.