Store JSON Schemas of all used schemas in a container also in the container

[apirogov]

This enables validation even if the Metador schemas are not available.

NOTE: the json schema export must be thoroughly tested, specifically whether the schema hashsum based id works as expected -

the schema hashsum should change iff:

• a plugin version changes
• the json schema operational definition changes (excluding e.g. title / description changes)
• the attached metador constant fields change
• any of these changes happen in a referenced parent or nested schema (thus, changing the hash, thus changing the reference)