Item12783: more reductions to first-time configure

   * Turn ={SafeEnvPath} into an expert option: on any remotely reasonable system, PATH for the www user should be safe in the first place. To allow us to hide this setting, remove the 'I guessed this' hint. Not particularly elegant but not a big deal, either.
   * Add colour hints to save/discard buttons to make them easier to spot; to achieve this, extend !ModalTemplate::_renderButton to allow us to specify custom classes
   * Get rid of status buttons up top more thoroughly
   * Make welcome message even more concise
   * Same for after-first-time intro message
      * Add buttons for common tasks. For now: change password, install extensions
   * Clean up the UI even further using JS:
      * Hide the validator toggle buttons -- there are no validation messages anyway
      * Hide the "I guessed this" warnings because they're redundant
      * Show the info texts by default, so people know what to do
      * Hide headings -- they don't help much with only two sections
      * Hide yet another summary of warnings


git-svn-id: http://svn.foswiki.org/trunk/core@17358 0b4bb1d4-4e5a-0410-9cc4-b2b747904278