Previously no timeout was used at all.
This surely lead to some usability issues in case of temporary network
problems.

Previously during the extension setup a connection was attempted once
and the success state of this attempt was memorized.
In later search queries a stored failure caused the backend query to be
skipped.

This lead to two problems:
* Not all requests took the initial connection test result into account
  (i.e. some queries were skipped and some were not).
* The initial connection test result was not updated during the life
  time of the extension (i.e. until the next restart of Mopidy).
  Thus, a broken connection could never recover.

The listing was broken since commit 1e9ca37.
Now we enforce the string conversion for browse item names again.