* Add a Help button and text to the 3D alias configuration dialog
* Display KISYS3DMOD and internally defined KiCad path env vars
* Add a button to bring up the "Configure Paths" (env vars) dialog
* Remove the file name mapping feature from the resolver; this results in
the resolver always using the current definition rather than a possibly
outdated cache value.
* Paths defined via pcbnew->Preferences->Configure Paths are now included in
the 3D file browser's drop-down list except for KICAD_PTEMPLATES, KIGITHUB,
KISYSMOD, any paths resembling a URL, and any non-existent paths. When an
absolute path is shortened using one of these path aliases, let's say
'KISYS3DMOD' then the name appears in the pcb file as "${KISYS3DMOD}/blah.wrl".
If a user defines and actual environment variable with the same name, then
that user defined variable will have precedence over the internally defined
variable.
* Paths relative to the current project directory are no longer represented
as "some/path/to/file.wrl". For compatibility with previous KiCad versions
it shall always be stored as ${KIPRJMOD}/some/path/to/file.wrl.
* Various restrictions on alias path values have been removed since the
imposed restrictions could result in corrupted user data as aliases are
silently dropped.
* Overall the patch should improve back-compatibility by providing a ${ENV_VAR}
mechanism for supporting different model root directories and ensuring that
paths relative to KIPRJMOD are expressed in a way that is compatible with
earlier KiCad versions. This allows users more flexibility and the ability
to work in a way that ensures 3D model files can be correctly resolved in
earlier versions of KiCad. Users who do not care about back-compatibility
may prefer to use the newer alias system.