Fix error - assigning cells to double

blockedReactions was initially declared as a double. However,
model.rxns(i) is a cell and can't be assigned to a double. Fixed it by
declaring it as an empty cell array.
Fix faulty metabolite renaming

The metabolite renaming was incorrect. findRxnIDs was called with a
metabolite name as the second argument, wherein a reaction should have
actually been used. Replace with findMetIDs. Reactions were being
renamed, fix to replace only metabolites.
Change ambiguous variable names

Replac rxnNames with rxnList as model.rxnNames is different from
model.rxns, and model.rxns is used to select the subnetwork. Replac
metNames with metList, to avoid similar confusion.
Add the fields - rxnNames, rules and metCharge

Adds rxnNames, rules (which contains the binary representations whereas
grRules contains a string(cell) representation) and metCharge to the
subnetwork.
Merge pull request #27 from sriki18/master

Fix error - assigning cells to double