[Enhancement] Automatic Error Reporting, for ZeroNet, for Plugins and for Sites

It would be great to add automatic error reporting for ZeroNet core, for Plugins and for Sites.

Basically there should be a site that clients automatically report errors to, when they occurr with a standard ZeroNet/Plugin/Site version (we could check in some way that the user did not customize it).

* Each Plugin/Site specifies a site address to which errors are reported
* In such site errors are aggregated according to stack trace and to ZN/Plugin/Site version and the information found in the debug page is written to it, encrypted to the site owner/moderators
* Such sites could be hidden from the user view and be given an higher default space limit
* On error one could possibly redirect the user to the page of its error report and ask him to add some comments
* The user could be notified about possible comments or requests of site owner/moderators

## TODOLIST
- [ ] Create example site that can be cloned and to which reports can be submitted
- Insert error handler and submitter in
- [ ] ZeroNet core
- [ ] Plugin
- [ ] Sites `content.json` key `error_report_address`

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Sidenote: obviously the site should be named "ZeroError"

Start by defining the example site that accepts reports, then trace the ZeroNet core and Plugin error-handling entry points and the Sites content.json configuration. Done means a cloneable example site exists and error submission works for the core, Plugins, and Sites configured with error_report_address.

Vom Indexierungsmodell aus dem Issue-Text verfasst.