Support path syntax for project tasks

[kordejong]

It must be possible to create a hierarchy of sub-projects (tasks?). For example, one might spent time on the administration, design and implementation of a project:

20140902: 1: my_project/administration
20140902: 2: my_project/design
20140902: 5: my_project/implementation

Given this information it must be possible to query for the amount of time spent on the whole project, but also on tasks within the project (percentages?).

The hierarchy may be multiple levels deep.