PDF Output: Do not error out when subsetting fails

PDF Output: Do not error out when the input document uses a font that
cannot be subset, such as the Symbol font. Instead print a warning and
embed the full font. Fixes #1203449 [EPUB to PDF conversion fails](https://bugs.launchpad.net/calibre/+bug/1203449)
Fix deleting books in newdb
Fix adding of books in newdb
newdb: Fix reloading of content server on metadata.db change
newdb: calibredb add calibre file.ebook tested
newdb: basic testing complete
Add a button to clear the current virtual library easily
Allow Virtual Library removal confirmation dialog to be skipped
Scroll the list of tweaks when using the keyboard
pep8
Merge branch 'master' of https://github.com/cbhaley/calibre
Update mediapart.fr
Driver for Surtab Ventos

Fixes #1204885 [Trekstor Surftab not recognized](https://bugs.launchpad.net/calibre/+bug/1204885)
No names, No jackets by Armin Geller
Blindbuch by Armin Geller
Document the danger of using parse_css in the polish books container
Polish books: Fix @page rules being removed

Book polishing: Fix page margins being removed if an unused font was
found during subsetting of embedded fonts.
Update Spektrum der Wissenschaft
McAfee have fixed their SiteAdvisor rating
Content server: Fix search query not being fully sanitized in results page

Fixes #1205385 [Private bug](https://bugs.launchpad.net/calibre/+bug/1205385)