Hint pool dev

• Modified vector max pool to be able to pool at any size/stride.
• Vector max pool segfault bugfix.
• Added tests.
• Modified residual hints to be pooled after the residual is computed.
• Hint training schedule sticks with 0-12 hints at all stages now (used to be more hints at the beginning).
• Switched PWCNet freezing script to use the factory.
• Hint input modified to do vector pooling after getting residual hints.
• Hint evaluation script indexing bugfix + tests.