Improved HTML output of sidebarlogo and simplfied user interface

These are the most important changes and the reason for each change:
1. Changed application of stylesheets: Old version added a style-tag into the body which works in most browsers but violates HTML rules. New version now uses the style attribute instead or uses id or classes from the theme stylesheet. This method is preferred over inline styles.
2. Added an alt-tag option for the image since this is required by HTML.
3. Reduced the plugin to title, image and description. This allows the plugin to work using only styles found within the theme stylesheet and fits more closely to about boxes found on many blogs. Copyright and other information can easily be integrated into description providing more flexiblity and a more straight forward configuration interface at the same time. Another reason for this change is that without the style-tag a lot of extra configuration field are required to support styles for each element (copyright, contact, tagline, link, ...). This is overwhelming for most users. Since HTML is possible within the description block (a hint for this is given in configuration description) all field can be added easily by using very basic HTML.

I believe that these changes provides a good compromise between required features and complexity. Different to HTML nugget it already provides the basic formatting and elements of a common sidebar item (title, description block). With the option to provide a logo, it is definitely sufficient to provide an about box many blogs use. While more advanced options are possible, the average user is not overwhelmed by a large set of options. This is especially true after dropping the style-tag, thereby creating the need for a style configuration field for each extra element present in the plugin.

Oliver