Bug 978682 - First render of call log is not covering all the screen

Fixed bug where previous date group was not rendered until after the
next batch.

Change batch size to be based on group count instead of day count.

Increased first render size to accomodate larger screens.
Merge pull request #17043 from yor-mozilla-com/bug978682

Bug 978682 - Fixed bug where previous date group was not rendered until after the r=rik