Make the asset tree more flexible by changing Section to self referencing

[Gavin]

This is a very good idea and would make the asset tree depth that extra bit more flexible. This could be setup similar to the way an Asset can have as many depths of Sub Items as required.

Example:

• Company
  • Region
    • Site
      • Section

Company and Region are currently not catered for, while Section already has a Department.

This affects:

• Database schema.
• Asset tree taglib as accessed from the tree icon on the main nav.
• The asset tree import and export functions.
• Cascase deletion and updates.

Hence placing in future milestone for now.