Ditch support of node.js version <4.0.0

Gradually retiring old dependencies.

Leave auto approvals

Add new feature of leave auto approvals. Employees could be configured to have new leaves going directly into Approved status.

Bugfixes

Fixes for recently deployed new feature: cancelation before approvals.

Cancel unapproved leave requests

Allow employees to cancel leave requests that were not approved yet.

Introduce concept of schedule

Now it is possible to define custom schedule for entire company or individual employees: configure working and non-working days.