Disallow inclusion of files from other papers

Make the file opening policy of the system compilers of texlive
prevents TeX from reading hidden files ( starting with a `.`) and paths
that, at some point, go to the parent directory.

The \BlueLaTeX custom texmf.cnf file prevents people from including
content from other papers (more precisely from other users' papers!)
and thus helps to avoid data leaks.

The paper will not compile if it contains somehting like:

```tex
  \input{../some-paper/main.tex}
```

or

```tex
  \include{./../some-other-paper/main.tex}
```

TeX documents are only allowed to include files present in the paper
directory or at standard TeX places on the system (system styles,
classes, ...).