Introduce new javascript tree based at Fancytree

[Klap-in]

See #254 and #230

• Introduces Fancytree as alternative to current dTree based index tree (first not default).
  • Can be enabled with temporary extra settings: treenew, treeold(default at the moment, will change) and treeboth (for testing).
  • dTree is deprecated, will be removed in time.
  • see #230 for features that are already implemented for Fancytree version
  • theming needs probably more effort (svg versions, how to add new custom skins,.. #245)
  • contextmenu and ToC are not supported (to be considered, needs more effort)

    • 244,

    • 246

• Lot of refactoring (which should not change functionality of the old functionality significantly...)
• Remove admin.php (as dTree is deprecated)