Update index server

[enkore]

• Fix IndexHTTPTest
• Document how to update identity properties (drop URL and alias), also add a test for that
• Update search endpoint to use the JSON API of the server
• Add search API to search for a bunch of contacts at once; update IndexContact to have the "matches" property to indicate which contact in the result set belongs to which part of the query
• Add API to query identity status
• Add API to delete identity entirely
• Reimplement MainIndexService (in progress...)
• Deduplicate retry logic
• Nullable IdentityStatus
• Fix MainIndexService test
• Perhaps create lower level tests for the new APIs (<-- most of the existing ones are actually for validating correct use and understanding of gson)

Fixes #600 and implements the new APIs discussed in #615 meeting.

[enkore]

@JoGir: Can you take a look at the IndexHTTP API?

[JoGir]

• Nullable IdentityStatus if not registered
• duplicate retry handling
• apply changes to IndexService

[audax]

I think the index server in the test-docker-container is not updated @rehwanne

[rehwanne]

I rebuilt the Container with new Versions of everything.