Implemented logic to save toggle items

[fenu28]

Changes made:

• Added onCheckedChangedListener to toggle items
• Added restoreToggleItemsState() to get back toggle items state in onCreate() of Settings.java
• Used sharedPreferences to save toggle items state. 1 denotes ON and 0 denoted OFF. This was much simpler than ArrayList logic
• Added two constants SWITCH_TWELVE, SWITCH_NOTIFICATION in Constants.java
• Removed SWITCH_TWENTY_FOUR from Constants.java because 24 hour switch state can be directly checked by 12 hour switch state
• Removed android:checked from toggle items in activity_settings.xml
• Improved code readability by removing unnecessary if else statements in Settings.java.
• Removed unnecessary imports from Settings.java

Things I learned:

• When/ when not to use ArrayList
• Git concepts because I messed up my git repo -_- with unnecessary push and commits

Fixes #33

[fenu28]

@HemangNakarani changes done as you suggested. Please review.

[HemangNakarani]

give @fenu28 5 points

[HemangNakarani]

give @fenu28 5 points