Fixed bugs in DatabaseHelper.java

- Checking whether or not string were empty using "isEmpty()" is not
  backwards compatibile with Android API 8, so now checks are done using
  the length() method

- Schema db insertion method did not pass the db object reference to the
  DAO and this caused the application to crash. Without the reference,
  the DAO attempted to create a new db object. Since schema insertions
  are only invoked when a database operation is already occuring,
  database access was locked, which caused the crash.

Signed-off-by: Byron Sanchez <bfs5030@gmail.com>
Added saveNote() as a state object method.

When the model state is set to Unlocked, saveNote will write the model
to the database. When the model state is set to Locked, saveNote will
not write the model to the database.

Signed-off-by: Byron Sanchez <bfs5030@gmail.com>