Fixes #51 - all-day-events

This patch should fix issue #51.
ssakasuma has already explained the problem in detail but has IMHO made a little fallacy.
It is correct that all-day events are stored with timezone UTC in the calendar database.
But from the calendar-widget-app's point of view the millis-field may not be recalculated/adopted, because this value is passed to the legacy calendar app (as explained out by mpost) and any modification would result in a change of the event's start / end dates.
The common construction of a joda-DateTime object by
```java
new DateTime(calendarCursor.getLong(2))
```
 is also necessary for all-day events
because they represent a day in the local timezone and proper ordering is needed (all-day events are always the first events within a day).
Thus the resulting solution is damn smaller: no special handling for all-day events anymore.