All day events should not require END TIME (as stated in manual)

[crysman]

All day events (Extension Settings -> Events are always all day -> YES) should not require END TIME column filled-in. In documentation, you say they shall be blank: (http://www.ballardsoftwarefoundry.com/gcalendarsync.html)

BUT when I let it blank, it pops up an error:

[itluzanky]

@Davepar Until fixed, I propose changing text in manual ("README").