Implement sharing of locations with other users

[gjwgit]

Description

A key feature of Solid Pods is the sharing of data with other users. This issue will implement the sharing functionality for the app. Support is provided by solidui including widgets that will provide sharing interfaces. See notepod and moviestar. Share locations will be displayed on my map using a different colour and the information box will show who is sharing the location with me.

Why

So that as a user I can decide to share locations and descriptions that I have created and "own" with other users, selectively..

Closing Criteria

Checklist for closing the issue:

• No errors from make prep
• All tests pass make qtest
• Demonstrate a user sharing several locations with another user

Alternatives

Additional Context

[gjwgit]

Rather than sharing single locations we will introduce the concept of a group of locations. Each location will be in some group. This avoids having all locations as separate files which introduces a performance hit querying for a single file at a time (unless we can query to return all files in one go). The we share groups of locations with others rather than single locations. Note that a group could be a single location so we don't lose that capability.