[landing] Making Dashboards the first/default tab

[john-bodley]

@hughhhh I think that the "Recently Viewed" tab still needs some refinement in terms of what we show there, and that user's may be somewhat confused, i.e.,

This PR changes the tab ordering and makes the "Dashboards" tab the first (and thus default) tab, which should seem more useful and familiar to users,

to: @hughhhh @mistercrunch

[codecov-io]

Codecov Report

Merging #4553 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4553   +/-   ##
=======================================
  Coverage   71.12%   71.12%           
=======================================
  Files         187      187           
  Lines       14780    14780           
  Branches     1083     1083           
=======================================
  Hits        10513    10513           
  Misses       4264     4264           
  Partials        3        3

Impacted Files	Coverage Δ
superset/assets/javascripts/welcome/App.jsx	94.44% <ø> (ø)	⬆️

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