Update version number for release (#114)

* Add unit tests for Budget class

* Add unit tests for Percentage class

* Add unit tests for Percentage class (supplement to previous commit)

* Add unit tests for AddBudgetCommand

* Add unit tests for AddBudgetCommandParser

* Add unit tests for UniqueBudgetList

* Add unit tests for JsonAdaptedBudget

* Add unit tests for SwitchBudgetCommand

* Add unit tests for SwitchBudgetCommandParser

* Update UniqueBudgetList to automatically set newly added budget as primary

* Add Budget field to Expense

* Update AddExpense method in AddressBook to suit the new Expense with a Budget field

Specifically,
step 1: check primary budget - if null, add default and set primary, if yes - do nothing
step 2: check expense's budget - if null, add to primary budget, if yes - add to corresponding budget
step 3: add expense to expenses list

* Cosmetic changes: Remove extra whitespace

* Check null parameters in JsonAdaptedBudget constructor

* Update EditCommand following the changes to Expense class (new budgetName field)

* Add method to check which expenses are within current budget period

Other changes:
- add method to update the proportion used
- check for duplicate expense before adding
- change expired condition to include end date
- increase default budget limit
- cosmetic changes to make code more concise

* Change Expense's budgetName field type from String to Description

* Update tests following the addition of budgetName field to Expense class

* Fix checkstyle errors in Main and Test

* Update Percentage class such that percentage larger than 1 will be treated as 1 instead of throwing an exception

* Fix unit test failures due to addition of Category field to Expense

* Fix checkstyle errors in Main and Test

* Update DG: Budget feature (with class, sequence, activity diagrams)

* Fix checkstyle errors

* Cosmetic changes

* Fix minor GUI bug

* Update version number for release

src/main/java/seedu/address/MainApp.java

@@ -38,7 +38,7 @@
  */
 public class MainApp extends Application {
 
-    public static final Version VERSION = new Version(0, 6, 0, true);
+    public static final Version VERSION = new Version(1, 2, 1, true);
 
     private static final Logger logger = LogsCenter.getLogger(MainApp.class);