Cleaned font cache code a bit
Cleaned font cache code a bit

  - Insertion only needs sub tree root and insertion node
      -> Does not need to drag cache object along the recursion
      -> Create and insert new glyph if required, no search required
         after insertion
  - Sperated tree insertion and tree balance
  - Propperly prefixed tree related functions with "tree_"

AgentD/sgui,AgentD/sgui,AgentD/sgui