Add sub-category

Add the ability to add a sub-category for areas that have sub-areas e.g. a production line that has seperate stations

Main Category: Car Assembly
Sub-Category: Motor Assembly Bench

Display sub-category indented into the [filter by category] view

e.g.

• Category 1

• Category 2

  • Sub-cat 1

  • sub-cat 2

• Category 3