Refactor of Entry, Note, Mood, Photo

- Entry is now Day (Mood moved to Note/new Entry)
- Note is now Entry
- Removed the useless canBeDeleted method from Day and Entry.
- Various comment fixes across al files

DB.java is still not working
Fixed some column names in DB.java

When refactoring all the other classes with AS I've inadvertently renamed also
these column names.
Removed a leftover Mood parameter from Day constructor
Refactored all the versions of DB.getEntry to DB.getDay
Refactored all the versions of DB.createEntry to DB.createDay
Refactored DB.deleteEntry to DB.deleteDay

I've also removed the throw InvalidOperationException, accordingly to the new
guidelines "Day and Entry can always be deleted"