sqs-browse: a lot of work to try to keep UI complexity down

Added the notion of controllers and a dispatcher which will queue up operations

internal/common/ui/events/errors.go

@@ -0,0 +1,16 @@
+package events
+
+import (
+	"github.com/lmika/awstools/internal/common/ui/uimodels"
+)
+
+// Error indicates that an error occurred
+type Error error
+
+// Message indicates that a message should be shown to the user
+type Message string
+
+// PromptForInput indicates that the context is requesting a line of input
+type PromptForInput struct {
+	OnDone uimodels.Operation
+}