Overhaul the Exporter-Functionality

[mutec]

The current way of how "exporters" work is pretty inflexible. Nowadays there's not only the WBB's content that should be imported, there are a lot of other packages generating (user generated) content, that could or should get imported in different cases. Since a jump to 6.0 is an obvious break and several things will get a state-of-the-art-touch, it might be a good point to re-design the whole export-feature.

At the moment it's the following scenario: You have to export from "WoltLab Suite Forum x.x", which already implies it's meant to be used for the forum-software only. Afterwards you have to use other exporters for other packages, partly performing the same basic-exports for users, user group options and other general stuff in order to match the data securely.

I'd suggest to improve the whole user experience while "importing"/exporting data towards this "migration": First, select the source-system:

Then provide several credentials:

Afterwards run several checks against the old system, and display what we're able to migrate:

Right before starting the migration we should adjust some additional settings in several cases:

Do the Migration.

Show a summary of migrated content afterwards, so the administrator can run a plausibility-check. Also a hint for refreshing data should be displayed.

The whole process should be developed based on the FormBuilder-API and in an open way, so everyone could easily extend the whole process by their data.