Fix relative imports

- Fix relative imports in base of is a package or not
- Fix not working notebooks
- Add notebooks to packages sources

Ipython created notebooks with python3 kernels

Changes in util.py

Add test grid

Add test cases for histogram in utils_test.py

cleaned 2-d grid methods in utils.py as we got them in grid.py

empty __init__.py in tests/ so build passes in local repo

Finished porting to Python 3

This reverts commit 14c0cfe5.

Used tool 2to3 to finish the porting to Python 3 plus some fixes by
hand.

Fixed missing bracket in utils_test.py

Port and test text module for python 3.5

Link aimacode/aima-data repository as a git submodule

Agents.py