Add Warning to KeeShare export

[OnSlbWXt]

Summary

In reference to #3045 please add a warning to the export and synchronize options, that the directory structure will not be preserved in the exported/synchronized database

Examples

Context

We did not know that the groups would be lost and started using the KeeShare feature and had our several hundred group sized Database be flattened into the DB root. We could restore, but it would have been nice to know that beforehand.

[droidmonkey]

The goal for 2.8.0 is to sync group structure and make KeeShare a first class "share group" feature. It sounds like you KeeShare'd your root group which is not encouraged. We do point out the non-sync of group structure in the documentation, but it would be nice to point that out in the GUI as well.

[OnSlbWXt]

Unfortunately I did not share my root group
Structure was like this:
Root
-> Network
-> Browser
-> [...]
-> Shared Group A (flattened .kdbx, when opened directly)
---> Foo
-----> Sub-Foo
---> Bar
-----> Sub-Bar
-----> [...]
---> [...]
-> Shared Group B (flattened .kdbx, when opened directly)
---> Baz
---> Bap
-----> Sub-Bap
-----> Sub-Baz
---> [...]

[droidmonkey]

Gotcha, that's a good thing, sharing root group is generally bad

[OnSlbWXt]

After our recovery I am facing the next issue:
When setting reconnecting a shared kdbx with "import" (instead of sync) it now deletes all my other entries. Backups are saving my ass again. But apparently I now can no longer synchronize my Databases at all ...

[droidmonkey]

You are hitting all the keeshare suck points.

#6477