Implemented more intelligent AI

1. picks a white connector
2. checks that the choice doesn't lose
3. tries not to complete any of opponent's triangles
4. tries to choose from a list of "optimal choices" (see PDF- 9 moves:
along the edge of the hexagon and 3 lines criss-crossing within).

Computer should try to satisfy all conditions, in that order- with the
1st being the most important and the last being the least.
Merge branch 'master' of https://github.com/Yisheng-G/cs61bl-proj1