- adds trillian API object to context
- improves request error logging pre and post validation
- use consistent request context throughout all GRPC calls
- improve validation of incoming UUID values
- disable swagger UI endpoint
- only print cacheable headers if response code is HTTP 2XX
- use GetLeavesByRange instead of deprecated GetLeavesByIndex API

Signed-off-by: Bob Callaway <bcallawa@redhat.com>

simplify upload command to reuse common PKI package across client & server

Some changes:
- import names (app -> api, logging -> log)
- Commands package (cmd -> app)