1. use [staticcheck](https://staticcheck.io/) to check the code, and fix some issues.
2. use `go fmt` to format the code.
3. use `go mod tidy` clean the go mod.
Notable refactoring:
- Use stdlib "context" in place of "golang.org/x/net/context"
- Go-kit no longer wraps errors, so we remove the unwrap in transport_error.go
- Use MakeHandler when setting up endpoint tests (fixes test bug caught during
this refactoring)
Closes#1411.
- Introduce kolide.ListOptions to store pagination params (in the future it can
also store ordering/filtering params)
- Refactor service/datastore methods to take kolide.ListOptions
- Implement pagination
