#2678 wrapper div of class columns added

[StephDriver]

On investigating, this bug only affected OLH theme.

The about section was unaffected due to padding provided by div class 'columns.'

Added a wrapper div of class columns to the issue_block.html template to gain same affect for this block.

Used a wrapper within homepage element because otherwise this would have required individual changes (e.g. to add this class) to both issue_top and issue_block journal elements which may be re-used elsewhere as not specific to homepage.

Closes #2678