feat: add "col" property in theme

[sstefoss]

Added "col" property in theme in order to set the default breakpoint value of a Column. Closes #72

[codecov[bot]]

Codecov Report

Merging #78 into master will not change coverage. The diff coverage is 100%.

@@          Coverage Diff          @@
##           master    #78   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          11     11           
  Lines          90     93    +3     
  Branches       23     24    +1     
=====================================
+ Hits           90     93    +3

Impacted Files	Coverage Δ
src/theme/theme.js	100% <ø> (ø)	:arrow_up:
src/theme/defaultTheme.js	100% <ø> (ø)	:arrow_up:
src/helpers/columnWidth/columnWidth.js	100% <100%> (ø)	:arrow_up:

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[aaronvanston]

Nice PR, thanks for spending the time to complete this! I will pull this down and test locally. Will merge ASAP! :)

[aaronvanston]

@sstefoss Apologies for the delay. I had been some testing and noticed some issues when running this via the storybook document. I will need to do some investigation to see what is going wrong (odd column stacking and height).

In addition We should also add documentation on this feature within both the react-flexa README.md and the Col readme. I'm happy to help with this if need be.

[aaronvanston]

The issue with the height looks to be an issue more with an older cached version of storybook rather than your changes. I will investigate further.