[fix #103] Check permission for paper settings

Only authors and reviewers should be allowed to see the paper settings
and roles.

This will be refined later when using the fine-grained permission
framework.
[imp #94] Add new system compilers

Adding common \LaTeX compilers makes it possible to compiler more
documents.
So, by default we now have:
 - pdflatex (default compiler)
 - latex + dvipdfm,
 - xelatex,
 - lualatex

\BlueLaTeX assumes that these tools are installed on the system and
does not check for their existence.

If problems arise on some platforms, we should have a look at how to
make it detect if these tools are present in a portable way (well,
problem is probably on windows, which has no `which` command, and I am
not aware of any similar command, help is welcome here).

This commit closes #94
Merge pull request #104 from satabin/fix/103/check-roles

[fix #103] Check permission for paper settings
Merge pull request #105 from satabin/feature/add-more-compilers

[imp #94] Add new system compilers
[imp #55] Improve configuration loading

The default values are now in a file named `application.conf` so that
keys are resolved with the local overrides for configuration. This makes
it possible to simplify configuration overrides when substitutions are
used. The keys using substitution in the default configuration must not
be overridden as well.

By making sure that the local files are loaded at last, we now that
their values will be taken over the default ones, as specified in the
HOCON file format.
Turn akka verbosity off

By default, akka logs any message that could not be delivered to an
actor which was shut down. This is a quite common situation in
\BlueLaTeX, and we do not want to be notified for this.