Added equals() and hashCode() methods in Note

Automatically generated with android studio (they should work fine)
Added equals() and hashCode() methods in Entry

Automatically generated with android studio (they should work fine)
Small improvement in two  SELECT statements in DB.java

The new version is more explicit (Explicit is better than implicit)
Small changes in the variable names of SQL stuff in DB
Added the time of creation to the Note objects

I've also updated everything that uses/creates a Note in DB.java
to manage also the newly created time field.
The Notes of each Entry returned by DB are now ordered

I've added an ORDER BY in the SELECT stataments so the note list
in each Entry is now ordered correctly from the oldest Note to
the newest one.
Created the new file AppConstants.java

This file will be used to save all the constants needed in multiple
places of the application or to store some one time settings.
I've also changed the model.Mood.getEmoteId() to use this newly
created file to store the file prefix.
Implemented Note.canBeUpdated() and canBeDeleted()
Added the Mood_TABLE with a some example Moods