This is issue 869 and is required for several reasons: 1) to make Inishell more
similar to MeteoIO, Snowpack, etc 2) because Qt6 is moving to CMake in
replacement of qmake 3) because it will "easily" allow creating native packages
for several platforms.

This layout should be well known and unsurprising to users, and the
ability to just cancel if something was changed by accident is also
nice.
Also, all windows now have reasonable minimum sizes.

Namely "open parent folder" and "delete file"

And minor cleanup

The IniFolderView would only remember the last path on double-clicks into the file system but not when using the toolbar - this has been fixed.

I always expect something to happen on Strg+F in the preview... so the find function has been implemented.

Outource some code instead of tripling it. Closing the preview via key
board is a bit more intuitive (strg+w closes one tab after the other
until it finally closes the main window).

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

This icon set is to be used on Mac.

Some icons were still not working, this has been fixed. The search paths for the application files has once more been tweaked to behave better with Linux usage. The ini files panel now shows the path centered, italic and on a neutral background. The pre-defined buttons roles have been set where possible/applicable. When a workflow external application run is fininshed, the application notifies the user (blinking taskbar icon, bouncing cursor, etc depending on the platform). The XML validation had a bug: it converted the bytestream to the local encoding when it must be to utf8. And finally, some more micro-optimizations.

This only works on Linux (following the XDG specification, see https://specifications.freedesktop.org/icon-naming-spec/icon-naming-spec-latest.html) so a fallback is provided for osX and Windows.We will try at some point to provide specific iconsets for Windows and osX.

Because there was no way to completely reset a Numbers panel (there can't not be a number in a spin box) this is now possible via a generic context menu in all panels. Restructure the menu a little to make these functions more clear

Settings page is loaded

Allow to load multiple INIs into the GUI via the context menu (like it was already possible for XMLs)

Use new settings wrapper for last visited INI folder and add context menu to open INI files and folders on the file system