Re: [GSOC 2016] persisting tabs across app restart

An idea: when restoreTab is called, instead of calling openTab, we could 
call modifyEventWithDialog instead.  In the persistTab call we can 
access and save the hashId for the given calendar item from aArgs.  Then 
in restoreTab we might be able to get that calendar item using the 
hashId (which would be used as the first argument passed to 
modifyEventWithDialog).  But I don't see yet how to use that hashId to 
get the item.

I see there is an itemById method on cal.hashedArray [1] but not sure 
how to get an array of calendar items to use it on (assuming I'm even on 
the right track here).

-Paul

[1] 
https://dxr.mozilla.org/comm-central/source/calendar/base/modules/calHashedArray.jsm#65