Customize [downloads] shortcode columns of 0

The downloads shortcode spits out div's with clear:both in order to force columns, but if one could make a column of 0 (zero) without them, it would permit CSS styling for a far easier responsive display.
Fix Last Month and Last week graphs. Closes #1853
Fix invalid date error. Closes #1850
Updated version and changelog
Fix merge conflict
Don't echo within apply_filters

'cause it no work.
Merge pull request #1861 from JustinSainton/patch-3

Don't echo within apply_filters
The only other instance of echoing w/in apply_filters

Happens to be a couple hundred SLOC prior to the last one.
Merge pull request #1862 from JustinSainton/patch-3

The only other instance of echoing w/in apply_filters
Merge branch 'patch-1' of https://github.com/Ipstenu/Easy-Digital-Downloads into Ipstenu-patch-1
Check for 0 first
Merge branch 'master' of github.com:easydigitaldownloads/Easy-Digital-Downloads
Fix merge conflict