Connect backend refactor (#801)

* Move connect backend code to its own package
* Move errors into the connect package
* Add NewBackend func

pkg/api/errors.go

@@ -7,12 +7,10 @@ import (
 var (
 	errNotConnected         = errors.New("Not connected")
 	errNotPermitted         = errors.New("Not permitted")
-	errConnStringRequired   = errors.New("Connection string is required")
 	errInvalidConnString    = errors.New("Invalid connection string")
 	errSessionRequired      = errors.New("Session ID is required")
 	errSessionLocked        = errors.New("Session is locked")
 	errURLRequired          = errors.New("URL parameter is required")
 	errQueryRequired        = errors.New("Query parameter is required")
 	errDatabaseNameRequired = errors.New("Database name is required")
-	errBackendConnectError  = errors.New("Unable to connect to the auth backend")
 )