"Yearly holiday hours" should be an attribute of the city work calendar

[jaragunde]

The number of holiday hours associated to a year is currently a configuration parameter. This causes trouble when this figure changes due to e.g. new company agreements.

This number should be an attribute of the work calendar (in the data model, that's currently named "city") and should be dependent of the year, so one city can have a different number of holiday hours on different years.

[jaragunde]

Also, the holiday hours assume that a standard journey is 8 hours per day * 5 days per week, and calculates the proportional number of hours for a user according to their assigned journey. It's undesirable to have this kind of hard-coded values in the system.

We should make this part of the configuration explicit too, e.g. "Madrid" -> 2018 -> 8h standard journey -> 184h holidays, "Paris" -> 2018 -> 7h standard journey -> 161h holidays