Initial Commit
Load data source successfully and switch & update the new data source successfully.
Added a place holder cell for table view when loading “failed” the data source.
Replaced the tableview datasource with OAArrayDataSource.
Integrated UITableViewDataSource and UITableViewDelegate into OAArrayDataSource and added a placeholder view for tableview when loading failed data source.
Added ignore file.
Added some descriptions for OAArayDataSource class.