breakpoints 7.x-1.2

Changes since 7.x-1.1 (11 commits):

• #2257855 by ron_s: Added Conflict with image styles machine name max length.
• #2210159 by Bags | lmeurs: Fixed Only one multipier defined causes notices, warnings and errors.
• export formatting
• #2203053 by jibize: Added Make Breakpoints compatible with Configuration module.
• Fixed warning whith empty breakpoint group
• #2187559 by marcvangend: Added Multipliers cannot be defined in theme's .info file.
• #2075595 by WarrenK: Fixed Documentation needs clarification.
• #1869968 by jamienotweet: Fixed Can't add/delete theme breakpoints.
• Allow empty media queries
• #1827756 by das-peter: Fixed export functionality.