feat(strict mode): adding strict mode flag to all js files

the flag must be in all src and test files so that we get the benefit of
running in the strict mode even in jstd

the following script was used to modify all files:

for file in `find src test -name "*.js"`; do
  echo -e "'use strict';\n" > temp.txt
  cat $file >> temp.txt
  mv temp.txt $file
done