Add 'virtual' keyword for functions in OptimizationTask.
Add 'virtual' keyword for functions in OptimizationTask.

Adding 'virtual' keyword for an inherited virtual function is good
practice because it will let the users know where the function
comes from.

pjwilliams/mosesdecoder,alvations/mosesdecoder,moses-smt/mosesdecoder,alvations/mosesdecoder,tofula/mosesdecoder,pjwilliams/mosesdecoder,moses-smt/mosesdecoder,hychyc07/mosesdecoder,tofula/mosesdecoder,alvations/mosesdecoder,hychyc07/mosesdecoder,hychyc07/mosesdecoder,hychyc07/mosesdecoder,hychyc07/mosesdecoder,KonceptGeek/mosesdecoder,alvations/mosesdecoder,pjwilliams/mosesdecoder,moses-smt/mosesdecoder,emjotde/mosesdecoder_nmt,alvations/mosesdecoder,tofula/mosesdecoder,moses-smt/mosesdecoder,emjotde/mosesdecoder_nmt,moses-smt/mosesdecoder,KonceptGeek/mosesdecoder,moses-smt/mosesdecoder,pjwilliams/mosesdecoder,alvations/mosesdecoder,hychyc07/mosesdecoder,alvations/mosesdecoder,alvations/mosesdecoder,tofula/mosesdecoder,KonceptGeek/mosesdecoder,KonceptGeek/mosesdecoder,tofula/mosesdecoder,emjotde/mosesdecoder_nmt,hychyc07/mosesdecoder,emjotde/mosesdecoder_nmt,KonceptGeek/mosesdecoder,moses-smt/mosesdecoder,hychyc07/mosesdecoder,tofula/mosesdecoder,moses-smt/mosesdecoder,alvations/mosesdecoder,emjotde/mosesdecoder_nmt,emjotde/mosesdecoder_nmt,pjwilliams/mosesdecoder,tofula/mosesdecoder,pjwilliams/mosesdecoder,alvations/mosesdecoder,tofula/mosesdecoder,emjotde/mosesdecoder_nmt,moses-smt/mosesdecoder,hychyc07/mosesdecoder,emjotde/mosesdecoder_nmt,KonceptGeek/mosesdecoder,KonceptGeek/mosesdecoder,moses-smt/mosesdecoder,hychyc07/mosesdecoder,KonceptGeek/mosesdecoder,KonceptGeek/mosesdecoder,moses-smt/mosesdecoder,emjotde/mosesdecoder_nmt,tofula/mosesdecoder,pjwilliams/mosesdecoder,tofula/mosesdecoder,pjwilliams/mosesdecoder,tofula/mosesdecoder,pjwilliams/mosesdecoder,alvations/mosesdecoder,pjwilliams/mosesdecoder,emjotde/mosesdecoder_nmt,KonceptGeek/mosesdecoder