Adds tabWidth prop to component

[sudolibre]

• Adds tab width prop to allow user to specify tab width as a number or string e.g. 165 or “165”. Also allows user to specify relative percentage width e.g. “20%”
• Dry up repeated tab width calculations in JSX by holding pre-calculated value in state

[codecov[bot]]

Codecov Report

Merging #47 into master will decrease coverage by 14.28%. The diff coverage is 6.66%.

@@             Coverage Diff             @@
##           master      #47       +/-   ##
===========================================
- Coverage   77.35%   63.07%   -14.29%     
===========================================
  Files           6        6               
  Lines          53       65       +12     
  Branches       11       15        +4     
===========================================
  Hits           41       41               
- Misses          9       16        +7     
- Partials        3        8        +5

Impacted Files	Coverage Δ
src/components/MaterialTabs.js	43.9% <6.66%> (-18.17%)	:arrow_down:

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[sudolibre]

needs a few more changes