#145 ignore empty questions inserting editing intents

[Miguel-Alves]

According to the needs of #145, this PR is solving the problems described.

• Now, when inserting or editting an intent, the user can leave empty ballons (as longs as they are not the only content), so it continues to stimulate him to add more content;
• Empty ballons are not saved to the database anymore;
• If present, empty balloons are removed from the utters upon loading;

This Pull Request resolves #145