Switches to negroni and gorilla/mux for routing

[prydonius]

This removes the go-swagger server. Negroni and gorilla/mux will allow
for easier handling of middleware.

[codecov-io]

Codecov Report

Merging #358 into master will decrease coverage by 0.73%.
The diff coverage is 83.94%.

@@            Coverage Diff             @@
##           master     #358      +/-   ##
==========================================
- Coverage   88.41%   87.67%   -0.74%     
==========================================
  Files          17       18       +1     
  Lines         820      844      +24     
==========================================
+ Hits          725      740      +15     
- Misses         61       68       +7     
- Partials       34       36       +2

Impacted Files	Coverage Δ
src/api/middleware/incluster.go	100% <100%> (ø)
src/api/handlers/charts/charts.go	100% <100%> (ø)	⬆️
src/api/handlers/healthz.go	100% <100%> (ø)	⬆️
src/api/handlers/repos/repos.go	63.15% <58.33%> (-5.86%)	⬇️
src/api/handlers/releases/releases.go	96.87% <95%> (-3.13%)	⬇️

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