Merge pull request #13 from pbs/LUN-1133

mas
LUN-1135 : Display credit even if image is under 200px wide
Merge pull request #14 from pbs/LUN-1135

Pull request
LUN-1131 -- set the ForeignKey to None if ThumbnailOption is deleted
LUN-1131 -- added migration
Merge pull request #15 from pbs/LUN-1131

LUN-1131 -- set the ForeignKey to None if ThumbnailOption is deleted
LUN-1134 -- logic and css styling to fix small images center alignment in the right rail
Merge pull request #16 from pbs/LUN-1134

LUN-1134 -- logic and css styling to fix small images center alignment i...
LUN-1139 : Fix image followed by text plugin breaking layout
Merge pull request #17 from pbs/LUN-1139

LUN-1139 : Fix image followed by text plugin breaking layout
LUN-1133 : Fix centering image and credit displayed next to image, code refactoring