Added concrete CRUD methods to DBManager
Removed instance CRUD methods from CategoryManager, StoresManager, ReceiptsManager
Added StringUtil class
Added DateConvertor class
Added CategoryForm class and CategoryForm.fxml UI definition file
Removed embedded manyToOne join column in Category class for the parent property and replaced with Integer type.
Modified ReceiptForm to handle Category.parent as an Integer instead of a nested Category
Added bank.properties file to control importing