Utility: rework Debug and friends to have all statics local.

Saves a bit in the symbol table and also makes the public interface a
little bit clearer. Removed default argument in setOutput() functions,
as it was essentially useless (was setting the output to the same
value). Also updated the documentation a bit.
TestSuite: anonymize unused variables.

Also catched by MSVC.
Utility: make the enum value more readable.
PluginManager: open the manager in nonexistent dir to avoid test failure.

Don't know why this doesn't happen on Linux, but with MSVC the manager
is opened in directory which contains all plugins and thus list also
the non-static ones.
Utility: disable -Wold-style-cast only on MinGW GCC.
Utility: fix Directory::list() on Windows.

We need to append wildcard to actually show anything.
Utility: fix Directory::rm() for directories on Windows.
Utility: fix Directory::fileExists() for directories on Windows.
Utility: create CorradeUtilityTestLib as small as possible.

Avoids weird issues on MSVC with two independent instances of Debug
class when doing tests for Utility library.
Utility: cleaned up and tested Directory::home().

Clearly separated Unix/Windows/other implementation, testing that
(hopefully) ubiquitous files/dirs are present in the returned directory.
Utility: cleaned up and tested Directory::configurationDir().

Making it XDG-compilant on Linux and BSD, testing on Linux and Windows
for presence for (hopefully) ubiquitous files and directories. Also
removed the ugly boolean parameter -- except for the boolean trap, the
default was harmful and this should be done explicitly rather than
implicitly.
Utility: cleaned up Directory::list().

More clearly separated the implementations.
Utility: mark some test files as "binary" to preserve EOL issues with Git.

We don't want to convert line endings for files which need to be tested
for (non-)presence of CR character.