FR: Please reconsider marking all styles !important

It's very hard to tweak styles in the site-specific plugin's CSS or adding a theme when all of them are marked with `!important`. Maybe I'm missing something, but all style selectors are quite specific (all start with `.syntaxhighlighter`), so there is no apparent reason to do that. Removing them all from shCore.css and shDefault.css did not in fact change rendering.

Existing users' schemes would not be affected, as they have been forced to (ab)use `!important` anyway.

Start by inspecting shCore.css and shDefault.css, focusing on the !important declarations in the style selectors. Remove the declarations and compare the rendered output to confirm it does not change. Done means site-specific CSS and themes can override these styles without requiring !important.

Written by the indexing model from the issue text.