Issue 18: Added a popup to modify table columns (#31)

Added a new popup to modify the columns of the table. With this new popup, the user can:

- Show and hide columns
- Move columns around
- Add new columns which are derived from the value of an expression
- Delete columns

Also got the overlay mechanisms working.

cmd/dynamo-browse/main.go

@@ -22,6 +22,7 @@ import (
 	"github.com/lmika/audax/internal/dynamo-browse/ui"
 	"github.com/lmika/audax/internal/dynamo-browse/ui/keybindings"
 	"github.com/lmika/audax/internal/dynamo-browse/ui/teamodels/styles"
+	bus "github.com/lmika/events"
 	"github.com/lmika/gopkgs/cli"
 	"log"
 	"net"
@@ -72,6 +73,8 @@ func main() {
 		dynamoClient = dynamodb.NewFromConfig(cfg)
 	}
 
+	eventBus := bus.New()
+
 	uiStyles := styles.DefaultStyles
 	dynamoProvider := dynamo.NewProvider(dynamoClient)
 	resultSetSnapshotStore := workspacestore.NewResultSetSnapshotStore(ws)
@@ -93,8 +96,10 @@ func main() {
 	itemRendererService := itemrenderer.NewService(uiStyles.ItemView.FieldType, uiStyles.ItemView.MetaInfo)
 
 	state := controllers.NewState()
-	tableReadController := controllers.NewTableReadController(state, tableService, workspaceService, itemRendererService, *flagTable, true)
+	tableReadController := controllers.NewTableReadController(state, tableService, workspaceService, itemRendererService, eventBus, *flagTable)
 	tableWriteController := controllers.NewTableWriteController(state, tableService, tableReadController, settingStore)
+	columnsController := controllers.NewColumnsController(eventBus)
+	exportController := controllers.NewExportController(state, columnsController)
 	settingsController := controllers.NewSettingsController(settingStore)
 	keyBindings := keybindings.Default()
 
@@ -106,6 +111,8 @@ func main() {
 	model := ui.NewModel(
 		tableReadController,
 		tableWriteController,
+		columnsController,
+		exportController,
 		settingsController,
 		itemRendererService,
 		commandController,