Added Custom ID annotation, option to define one of your model's columns as secondary id

[yoavi2]

Added Custom ID annotation, option to define one of your model's columns as secondary id (Thus adding the option to use the server's id type such as String) for updating existing objects, with the same server id, that were retrieved from the server (objects with a different server id will be inserted normally)

Usage example:

@Table(name = LocationEntity.TABLE_NAME, id = BaseColumns._ID, customIdName = LocationEntity.OBJECT_ID)

the Column is defined the same (we use String in the example):

    @Column(name = OBJECT_ID,
            notNull = true,
            unique = true,
            onNullConflict = Column.ConflictAction.FAIL)
    public String objectId;