[Experimental] AppHeader.vue: use a range date picker

[Tofee]

This is a quick and dirty implementation of a range picker, to illustrate my comment https://github.com/owntracks/frontend/issues/43#issuecomment-1243020903 about date picker.

For my own use it seems to work, but it's probably not what you'd want to merge right now...

[Tofee]

If you want to have this merged at the very least remove the vue-ctk-date-time-picker dependency :)

The change has been done, do I need to do something else to mark the requested change as "handled" ?

[Tofee]

Superseeded by https://github.com/owntracks/frontend/pull/116

[jpmens]

@Tofee thank you for your contribution, even if it has been superseded; much appreciated!