Support of AspectJ language

Support of AspectJ language as discussed here: #968.
AspectJ files are currently recognized as Java files.
They are currently the only language with the .aj extension (thus no conflicts).

Some examples on GitHub:
https://github.com/Migueli/AspectJ
https://github.com/migue/blog-examples
https://github.com/eclipsesource/com.eclipsesource.tycho.aspectj.demo

I added two sample codes.