[mkcal] Check for read/write capability using QFileInfo

Previously, QDir::isReadable() was used.  We should ensure that we
have both read and write capability, using QFileInfo.  This is also
more accurate, as it will work if we have Group permissions.
Merge pull request #4 from chriadam/gread

[mkcal] Check for read/write capability using QFileInfo
[mkcal] Add start and end dates to timed alarms
Merge pull request #5 from pgerdt/update-timed-alarms

[mkcal] Add start and end dates to timed alarms