Add go report card and gofmt files

[maciaszczykm]

Added Go Report Card badge to README.md with following link: https://goreportcard.com/report/github.com/kubernetes/dashboard

Used gofmt on unformatted files. Fixed few golint issues.

Kubernetes core also uses Go Report Card.

[codecov-io]

Current coverage is 83.62%

Merging #500 into master will not affect coverage as of 1413951

@@            master    #500   diff @@
======================================
  Files           84      84       
  Stmts          696     696       
  Branches         0       0       
  Methods          0       0       
======================================
  Hit            582     582       
  Partial          0       0       
  Missed         114     114       

Review entire Coverage Diff as of 1413951

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[bryk]

Nice! Thanks. LGTM :)