Further optimization

[wongjiahau]

Optimized the permutator code by binarizing slots.
So a global dictionary to refer slot with binarized slot is needed. (they shall be referenced using SID, the slot identifier)
Could consider storing all info of a slot within one or two integer.
E.g.
First seven bit(max=128) use to identify subjects
Next two bit(max=4) to identify slot type (L/T/P)
Next six bit(max=64) to identify slot number,
Next three bit(max=8) to identify day (Mon/Tue ... )
And so on, and so forth