Fix typo.

Fix for: 76a0a725ad4501a14998b528eb1a856239d47e8c.
Rename the key to match its purpose.

Fix for: 55018fc140c2015c9bc99479a2fccda5255a6e4c.
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.
Rename the method to project
Remove the parameter - it's not necessary.
Move the #first method to the project method.
Delegate name to a project.
Rename the method to 'find_project'

For now it's enough, we don't find out projects by any other criteria.
Remove handling the exception.
Inline the #week method.
Inline the #create_time_entry method.
Use the #invalid method for getting invalid time entries.