swarm/storage/feeds: removed capital Feed throughout

cmd/swarm/feeds.go

cmd/swarm/feeds_test.go

cmd/swarm/main.go

swarm/api/api.go

swarm/api/client/client.go

swarm/api/http/server.go

swarm/api/http/server_test.go

swarm/api/manifest.go

swarm/network/README.md

swarm/storage/feeds/cacheentry.go

swarm/storage/feeds/error.go

swarm/storage/feeds/feed.go

swarm/storage/feeds/handler.go

swarm/storage/feeds/handler_test.go

swarm/storage/feeds/lookup/lookup.go

swarm/storage/feeds/request.go

swarm/storage/feeds/request_test.go

swarm/storage/feeds/sign.go

swarm/storage/localstore_test.go

swarm/testutil/http.go