#14 Improved category codes

[kaptijnr]

Category codes are very useful, but could be improved.
User-defined attributes with a user-defined drop-down list
of values makes the usage much easier. A hierarchy of
values even more. Filtering must be possible, sorting
probably also.

My company currently uses a four character category
code. One character for type of billable/non billable
hours, one for type of activity, one for cost-of-quality
attribute and one free character, mostly used for
grouping a set of tasks. The above mentioned feature
makes this much easier to use and maintain.