Improve GetBoards and getDefaultBoard (#22981)

Change 
`GetBoards(ctx context.Context, projectID int64)`
to
`(p *Project) GetBoards(ctx context.Context) (BoardList, error)`

`getDefaultBoard` is same.

models/project/board.go

@@ -229,14 +229,14 @@ func UpdateBoard(ctx context.Context, board *Board) error {
 
 // GetBoards fetches all boards related to a project
 // if no default board set, first board is a temporary "Uncategorized" board
-func GetBoards(ctx context.Context, projectID int64) (BoardList, error) {
+func (p *Project) GetBoards(ctx context.Context) (BoardList, error) {
 	boards := make([]*Board, 0, 5)
 
-	if err := db.GetEngine(ctx).Where("project_id=? AND `default`=?", projectID, false).OrderBy("Sorting").Find(&boards); err != nil {
+	if err := db.GetEngine(ctx).Where("project_id=? AND `default`=?", p.ID, false).OrderBy("Sorting").Find(&boards); err != nil {
 		return nil, err
 	}
 
-	defaultB, err := getDefaultBoard(ctx, projectID)
+	defaultB, err := p.getDefaultBoard(ctx)
 	if err != nil {
 		return nil, err
 	}
@@ -245,9 +245,9 @@ func GetBoards(ctx context.Context, projectID int64) (BoardList, error) {
 }
 
 // getDefaultBoard return default board and create a dummy if none exist
-func getDefaultBoard(ctx context.Context, projectID int64) (*Board, error) {
+func (p *Project) getDefaultBoard(ctx context.Context) (*Board, error) {
 	var board Board
-	exist, err := db.GetEngine(ctx).Where("project_id=? AND `default`=?", projectID, true).Get(&board)
+	exist, err := db.GetEngine(ctx).Where("project_id=? AND `default`=?", p.ID, true).Get(&board)
 	if err != nil {
 		return nil, err
 	}
@@ -257,7 +257,7 @@ func getDefaultBoard(ctx context.Context, projectID int64) (*Board, error) {
 
 	// represents a board for issues not assigned to one
 	return &Board{
-		ProjectID: projectID,
+		ProjectID: p.ID,
 		Title:     "Uncategorized",
 		Default:   true,
 	}, nil

routers/web/org/projects.go

@@ -313,7 +313,7 @@ func ViewProject(ctx *context.Context) {
 		return
 	}
 
-	boards, err := project_model.GetBoards(ctx, project.ID)
+	boards, err := project.GetBoards(ctx)
 	if err != nil {
 		ctx.ServerError("GetProjectBoards", err)
 		return

routers/web/repo/projects.go

@@ -300,7 +300,7 @@ func ViewProject(ctx *context.Context) {
 		return
 	}
 
-	boards, err := project_model.GetBoards(ctx, project.ID)
+	boards, err := project.GetBoards(ctx)
 	if err != nil {
 		ctx.ServerError("GetProjectBoards", err)
 		return