API to download/export account data

[dmitrizagidulin]

Create an API to enable users to download or export their account data. Useful for backing up data, or for moving data to a server that doesn't support an alternate 'copy'/migrate mechanism.

Note: This issue is related but separate from #12 - Enable users to migrate/copy their accounts to another server.

Open considerations:

• As @csarven mentioned, everything in the user's account should be exportable. What should the UI look like, for the user to select which data/containers they want exported?
• What format will the user's data be in? (see #11 - Implement/ensure Portability of user data)

To do:

• get consensus on the account export API
• determine the format of the exported data (see #11 - Implement/ensure Portability of user data)
• implement on ldnode - create issue
• add an 'Export Account' link to the profile-editor app

(Moved from solid/solid-spec#68)

[dmitrizagidulin]

See also: Packaging on the Web (W3C Editor's Draft) spec.

[RubenVerborgh]

Can we just expose that as an LDP interface, such that we do not have to invent a new API?
Then we only need to agree on the document/data structure of the LDP interface.