Subscribing and unsubscribing from series
Serie subscriptions

* A user id can be specified when (un)subscribing
* Refactored DAO.getOrgUnits method signature slightly
* Expanded unit tests
* Cleaned up jsdocs
Serie subscribing followup

* Move user defaulting to API
* DAO.getUserCalendar returns events
Merge branch 'subscribe' of https://github.com/fronteerio/grasshopper into subscribe
Small documentation fixes for default statements in JSDocs