Apply a Copyright comment to all Java source files in IntelliJ

To apply a Copyright comment to all Java source files in IntelliJ, do as follows:

IntelliJ IDEA -> Preferences...

Copyright -> Copyright Profiles

Add a profile as follows:

```
Copyright 2016 the original author or authors.

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.
```

In `Copyright`, select one for `Default project copyright`.

Add a scope.

Finally, apply the Copyright as follows:

`src/main/java` -> Update Copyright...
`src/test/java` -> Update Copyright...

Reference:
https://www.jetbrains.com/help/idea/2016.1/generating-and-updating-copyright-notice.html