Also cleans up the POST interface in general. No more paths in the URL,
all relevant details go into the json now.
Renames /~link/add to /~link/save to match the +action tag.
As such, format for /~link/save is:
{path: '/some/group', title: 'Some title', url: 'https://urbit.org/'}
Format for /~link/note is:
{path: '/some/group', url: 'https://urbit.org', udon: 'This is cool.'}
link-server-hook exposes (parts of) the link-store over eyre, on the
condition that the client is authenticated as the host ship.
link-webext as committed is a very minimal web extension. When its
toolbar button is clicked, it saves the current webpage to /private
in the link-store.
In the future, this should support choosing a target to save to,
highlighting already-saved pages, and many other features.
