Share SP selection logic with HTTP

[hannahhoward]

What

After we improve SP Selection logic with #92 for GraphSync (probably just the initial version), we should port this logic over to the HTTP protocol. (#193)

Implementation

Somewhat open ended -- let's collect the bare minimum information needed to match whatever we're currently aiming to collect with graphsync (I think just correctness for starters), and use it to put the PriorityWaitQueue into the HTTP selector. In this case, there's no "connect" step so we're just ranking all the providers at once and then selecting one semi randomly.