Template language: Add a new function (group_re) to use grouping regular expressions with groups, where you can replace the matched groups with result of another template

Merge branch 'master' of https://github.com/cbhaley/calibre
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UI for new Add Cover tool
Edit Book: new tool to easily add a cover to the book. It automatically generates the HTML wrapper and takes care of marking the covers files as covers in the OPF.
Update Deadspin
Add a tweak to change the font size in the template editor