1. Adds <property name="separateLineBetweenGroups" value="true"/> to CustomImportOrder to enfore blank line between imports groups.
2. Uses checkstyle 6.5, which fixed a bug of "CustomImportOrder checks import sorting according to ASCII order instead of case-insensitive alphabetical order".
The checkstyle.xml is a slightly modified version of the upstream Google
checkstyle configuration. All changes have comment describing them.
Lots of warnings were corrected. Examples is the only project that has
warnings still, as the necessary changes require some thought.