[Feature request] Avoid double import of GPX-files

[update-freak]

Hi developer,

I import all my GPX-file (about 200) from a folder.
Accidently I imported them again after I did the update to v.0.12.0.
So maybe it would be good to have a import check to avoid double import, e.g. depending on name etc. a message:
"Track XY already exists. Are you sure to import this track" -> Yes, to still import and No, to skip the import of this single file.
This should then also work for importing a whole folder with multiple files.

[update-freak]

and I think it would makes to have also the following option in the settings how to handle the import of double tracks:

• skip all double found tracks while the import => with this setting it's still possible to select whole folders with large amount of GPX-files
• raise the message while importing and a track is already there => message as in my first post (skip or import)