Improve the Wiki Administration

See http://design.xwiki.org/xwiki/bin/view/Proposal/Administration9x

Problem

• Some sections are hard to find since they are not in the corresponding category
• Some sections are hard to reach, although they are used often

Changes

• Reorganisation:
  • prioritising often used sections to be displayed at the top of categories
  • advanced and occasionally used sections are not that visible
• Regrouping: grouping related sections together with the usage of tabs
• Collapsable menu: in order to limit the scroll and display just the relevant category, simplifying the visible options
• Hints: added descriptive hints for all the options in order to clearly describe them and limit the ambiguity / need for documentation
• Default values / Placeholder / Inherited: clearly presented the default (inherited) value and providing placeholders on the format the values need to be
• Styling standardisation (headings, full width, buttons): have a consistent styling for sub-sections presentation and actions
• Title area + global/wiki/page: adding visible hints for categories and clearly stating the type of administration