Fix #1367221 [Tag management window larger than display](https://bugs.launchpad.net/calibre/+bug/1367221)
Update Strategy+Business

Fixes #1367347 [Private bug](https://bugs.launchpad.net/calibre/+bug/1367347)
Cover Grid: Dynamically adjust the size of the in memory cover thumbnail cache based on the window size to ensure flicker free rendering even on very large screens. Fixes #1367211 [cover grid continuously redraws covers](https://bugs.launchpad.net/calibre/+bug/1367211)
Initial implementation of colors/styles in cover generation
Cover generation work

Etch the text, add a gradient based style, allow styles to specify page
margins, more useful test() function that displays all color and style
variants at once.
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