Pets App v1.3

This release of the app does not contain any UI change.
The changes are made to the internal working of the code such as adding a ContentProvider to the app.
A custom ContentProvider named as PetProvider was added in this release to make the code more robust and secure.
The PetProvider also looks after the data validation in the app (cases such as negative weight and no gender).
This changes made in this version heavily rely on the use of URIs (Uniform Resource Identifier).