Clean up package dependencies

* Remove util.StringUtil, this can be done by commons-lang StringUtils
 * Remove util.ListUtility, this can be done by java.util.Arrays
 * Move all classes, except the ones used by fit, to fitnesse.util, or closer to where they're used.
 * Merge code from fitnesse.wikitext.Utils with fitnesse.html.HtmlUtil
 * Build system compiles fit, slim and the wiki server separately, to avoid polution between those packages.