Code formatting and cleanup (#442)

* Formatting, extract error messages
* More refactor
* Move errors to a separate file
* Add missing file
* Misc

pkg/api/errors.go

@@ -0,0 +1,19 @@
+package api
+
+import (
+	"errors"
+)
+
+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")
+	errPgDumpNotFound       = errors.New("pg_dump utility is not found")
+	errBackendConnectError  = errors.New("Unable to connect to the auth backend")
+)