Apache license headers and a license check

[yurishkuro]

Resolves #95

Headers are updated with the following script (source):

#!/bin/sh

find src -name "*.js" -print0 | xargs -0 \
gsed -i -e '/Permission is hereby granted, free of charge, to any person obtaining a copy/,/THE SOFTWARE.$/c\
// Licensed under the Apache License, Version 2.0 (the "License");\
// you may not use this file except in compliance with the License.\
// You may obtain a copy of the License at\
//\
// http://www.apache.org/licenses/LICENSE-2.0\
//\
// Unless required by applicable law or agreed to in writing, software\
// distributed under the License is distributed on an "AS IS" BASIS,\
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.\
// See the License for the specific language governing permissions and\
// limitations under the License.'