Updated sidebarlogo to produce valid HTML and provide a better user interface

1. alt attribute is now supported for logo and is set by default to comply to the HTML spec.
2. style tag is now longer produced. Instead, inline styles are defined for each element
   separately. Alternatively, CSS classes or id can be specified by prepending '.' or '#'.
3. User interface is simplified by putting all style definitions into subgroup 'styles'
   and advanced elements into group 'advanced elements and options'. Only the most basic
   option as description and logo are visible by default.
4. Ordering of elements is now enhanced with an option to enable and disable elements. The
   corresponding sequence option is also grouped into 'advanced elements and options'. By
   default only logo and description are visible.
5. A delimiter element is available now. It allows flow control for the logo if floating
   styles are defined.
6. German language file was added and English language file enhanced.

In summary, styles are now specified in a way that produces valid HTML. The image tag was
also changed to be HTML valid. The user interface was modified to make the plugin more
accessible for new users while preserving all options. User that need nothing more than
a simple about box better served now with the basic option while all other users can still
make use of all other elements.