Retain much tighter control of x-i2p-torrentlocation priorities

This guarantees that if a torrent-powered resource is available, it's prioritized in all cases and only on an error is a remote resource used. Speeds up page loads with big audio and video files. Also cleans up the code used to actually check x-i2p-torrentlocation values.

debian/changelog

+i2psetproxy.js (0.87-1) UNRELEASED; urgency=low
+
+  * Disable searching for i2p sites in non-i2p search engines
+  * Add contexts for i2pbote and Dispatch
+  * Remain in tighter control of x-i2p-torrentlocation priority
+
+ -- idk <hankhill19580@gmail.com>  Sat, 10 NOV 2020 1:33:50 -0400
+
 i2psetproxy.js (0.85-1) UNRELEASED; urgency=low
 
   * Fix a bug which was causing i2psnark to fail to isolate.