Fix #1255671: escaped parenthesis do not work in any search expression, and match_books does not escape parenthesis.
Enhancement #1255676: match books should update the thumbnail as well as the metadata.
Merge branch 'master' of https://github.com/cbhaley/calibre

Searching: Fix escaped parentheses not being correctly handled when
parsing search queries.

Match books on device: Fix parentheses in search expression not being
escaped. Fixes #1255671 [Match Books dialogue doesn't like parentheses](https://bugs.launchpad.net/calibre/+bug/1255671).

Match books on device: Fix thumbnail in device metadata cache not being
updated when matching books. Fixes #1255676 [[ENHANCEMENT] Match Books to add covers](https://bugs.launchpad.net/calibre/+bug/1255676).