Improved error message for unknown methods in BaseObject

In BaseObject.php line 95,
`list($operation, $attribute) = preg_split('/(?=[A-Z])/', $method, 2);`

preg_split would sometimes return only 1 element and try to assign it to a list of 2 elements, throwing an exception with an unclear message

Before: Notice: Undefined offset: 1 in .../Pomm/Object/BaseObject.php line 95
Now:    No such method "MyObject::foo()"