Fix Integer type to match java classes.

Here is a proposal to fix type linkage between java and python through the OGM.

In a nutshell, this allows to type properties using class Integer only: casting to classes BigInteger and Long is handled using size parameter.

Here is how it looks:

    >>> myInt, myLong, myBigInt = Integer(3), Integer(15), Integer(100)
    >>> print myInt.name_db, myLong.name_db, myBigInt.name_db
    Integer.class Long.class BigInteger.class