ikhal: improvements in event displaying

if one is looking at the details of an event and then selects another
event (or deselects the current one) the eventviewer disappears
ikhal: event editor (parly working)

all text only properties can be edited (type 'e' when viewing event
listi), hitting the save button actually saves the changed vcard (but
gives no visual hint at all), cancel button does nothing atm

start and end date can be edited, too, but won't be saved