New layout wip: button styling, hero component etc

[mipyykko]

• section headers should use Introduction component
• ContentWrapper to wrap a section or anything that needs responsive margins etc.
• Hero has multiple variations
• GeneralList and LinkBoxList are quite similar, now the front page hype section is using the former for a change, but can be changed back to links
• front page course selection is randomized from non-ended courses

[codecov[bot]]

Codecov Report

Merging #1240 (064f98b) into master (d82baf2) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1240   +/-   ##
=======================================
  Coverage   66.41%   66.41%           
=======================================
  Files         144      144           
  Lines        6036     6036           
  Branches     1433     1433           
=======================================
  Hits         4009     4009           
  Misses       1888     1888           
  Partials      139      139           

Flag	Coverage Δ
backend	66.41% <ø> (ø)

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