Fixes#201 and #144
* In the admin area of the style Flatmaas-Rev is no longer tried via stylesheet to include the image nib-logo.png.
* In the preview of the Leggero style "Posted by + time" is now displayed right-aligned - as in the blog.
* The heading for posts and pages has received its own CSS class "entry-title".
* In all three styles, both heading sizes are now displayed correctly; as in the blog, so in the preview.
* The publication date is truncated from h2 and now uses h6.
* Font size h4 can now also be conveniently set via BBCode button.
* Long single line code in leggero-v2 style is now wrapped when printing.
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