Removed repeated entries from resource drop-down search results

The repeated results where appearing because we inject repeated entries to
display the context of the current file/dir path. To avoid such elements
from appearing, we simply filter them out before displaying any results.

Fixes #100.
Made sorting URLs explicit

This is more user-friendly and we avoid ugly URLs by not using +/- signs.

Fixes #105.
Account for already-applied checks when switching sorting order

Fixes #104.