Allows the user to modify an object

Now the user has an option to update an existent object. If
a file is provided, the object's file will be updated. But if
the file is not provided, the object's file will not be
updated.

Change-Id: I67752c7881b0e6b4ab20b13cca94b24d292736d5
Implements: blueprint modify-object
Merge "Allows the user to modify an object"