Use the new syntax of hashes.

Also fix typo in the pending's description.
Rename period helper to current period.

It's more self explanatory.
Rename 'per project stats' to 'time per project' method.

And 'time per project' to 'calculate time per project' - this
method is used within the 'time per project method'
Delegate 'time entries' to a corowker.
Reformat the project model.
Add the pry gem.
Extract the code of getting query for all descendant ids into a method.
Move the query of getting descendant ids into the work unit model.
Move the query of getting projects related to given descendant it to the project model.