VALARM own class and schema definition & 'removeComponents' method in CalendarObject

[andresmatasuarez]

VALARM own class and schema definition

• Extracted VALARM schema definition to own file with useful class with setters.
• Implemented 'validate' method.
• Added tests for all this.
• plus: trimmed invisible spaces from lines with them.

  Added 'removeComponents' method in CalendarObject

• It receives an optional 'type' parameter.
• If set, removes all components of 'type' from this CalendarObject.
• Else, removes all components from this CalendarObject, regardless of their type.
• In both cases, it returns the components that were removed.
• If no component removed, returns undefined.

  Zero DURATION format fix

• A duration of zero seconds was being formatted to 'P' instead of 'P0D'