Allow for several default alarms for new events

[sarydrappeau]

Hi,
First of all thanks for this software,

I'd like to suggest the possibility for users to add several default alarms on new events.

Among the uncountably many ways to do this there are:

• one simple but not very canonical: add configuration options such as default_alarm_event2, ... to be parsed as the existing one,
• one neater way would be to allow the user to plug in several default_alarm_event options, but this would require some change in the config parser (currently it complains when it finds duplicates),
• another neat way maybe simpler to implement is to allow user to set up default alarm as a list e.g. defaut_alarm_event = 15m,1h. The parsing works fine at present, it would simply require a new validator type.

I'd be happy to propose an implementation if the maintainers let me know their preference.

SD