Add gutter styling in Bartik for new layouts

Problem/Motivation

Five layouts are being added with simple CSS and markup:

• layout_onecol
• layout_twocol
• layout_twocol_bricks
• layout_threecol_25_50_25
• layout_threecol_33_34_33

Currently, there are no gutters between the regions in these layouts. This causes content to bump into other region content.

Proposed resolution

Add gutters to Bartik for each of the layouts listed above.

Remaining tasks

• Add gutters for the new layouts that match Bartik's current styling.

User interface changes

N/A

API changes

N/A

Data model changes

N/A