Add gometalinter to CircleCI

remove unused variables detected by varcheck

[skip ci]

add tabs and search filter to new panel control

External auth refactor

Fix performance issue with running bra run for go run build.go build

Specify expected encoding for access/secret key

* master:
  changelog: adds note about closing #11613 and #11602
  fix: sign in link should have target self to trigger full page reload, fixes #11626
  codespell: exclude by words instead of files
  Use sort.Strings() (gosimple)
  Remove unused return value assignment (gosimple)
  Remove unnecessary fmt.Sprintf() calls (gosimple)
  Merge variable declaration with assignment (gosimple)
  Use fmt.Errorf() (gosimple)
  Simplify make() (gosimple)
  Use raw strings to avoid double escapes (gosimple)
  Simplify if expression (gosimple)
  Simplify comparison to bool constant (gosimple)
  Simplify error returns (gosimple)
  Remove redundant break statements (gosimple)

Code simplification (gosimple)

codespell: exclude by words instead of files