Make DefaultHandler plugin remount persistent

[elbakerino]

Make DefaultHandler plugin remount persistent, e.g. currently when an string schema has a default and it switches in isVirtual, the default value will be added again for e.g. number fields with an empty string / that where deleted by deleteOnEmpty.

May need another scope inside the store, can not be added to internal.

There should be an option, when a generator is used to "update data", to not apply default again - as default should maybe be done only at "create data".

Could be done together with #112

[elbakerino]

• added defaultHandled to Store.internals, from per-handler-state
• now remount persistent
• added prop doNotDefault to PluginProps, if doNotDefault is true no defaults are applied
• add readOnly support to default handling Fix readOnly and default handling #117

! todo: doNotDefault should/must respect "do-default" on e.g. new GenericList entries