Conversion: Handle shorthand CSS properties

Conversion: Fix bugs in the handling of shorthand CSS properties
such as font or border, which could cause some properties to
not be resolved correctly during conversion.
...
pep8
pep8
pep8
Use shorthand properties for margin, border and padding
Merge branch 'normalize'

EPUB/AZX3 Output: Use shorthand forms for margin, padding and
border CSS properties

Conversion: Fix a bug that could cause incorrect border values to be
used when cascading, shorthand border CSS is present.
Remove unused mount helper

Fixes #1225696 [Add patch to compile with CLANG](https://bugs.launchpad.net/calibre/+bug/1225696)
Handle broken code trying to set numeric columns with empty strings
Show a warning when copy to library is use don incompatible libs

Show a warning when attempting to copy books between libraries that do
no have the same set of custom columns. Fixes #1225484 [New feature: copy books between libraries with all custom metadata](https://bugs.launchpad.net/calibre/+bug/1225484)

Merge branch 'master' of https://github.com/cbhaley/calibre
Make default thumbnail quality 75
Improve quality of images manipulated by calibre. In particular improve images dropped or pasted into edit metadata. Note: Qt's default compression quality is 75, which is very low. Perhaps calibre's default doesn't need to be as high as 90, but it should be higher than 75. Perhaps this is a good place for a tweak.
Improve quality of images manipulated by calibre. In particular improve images dropped or pasted into edit metadata. Note: Qt's default compression quality is 75, which is very low. Perhaps calibre's default doesn't need to be as high as 90, but it should be higher than 75. Perhaps this is a good place for a tweak. (reverted from commit ae1255461f82656d83a78a5555f0810620449eba)