The header is required for msgfmt

`msgfmt` will not generate the compiled files without the header.
Because the header is hard-coded and cannot be changed or excluded
without causing problems, `sed` is used to make it consistent
across when generating while still leaving useful information
within the header.
Work on making MouseTrap available over PyPI

In order to make MouseTrap available over PyPI and installable
using `pip` and `easy_install`, a `main` function was needed so it
could be used as a wrapper and the input function for the script.

The MouseTrap version has also been added to `__init__.py` and is
available as `__version__` so other scripts can reference it.

The requirements are dynamically generated based on whether
Python 2 or Python 3 is being used.  Not all of the requirements
can be installed using `pip`, such as PyGObject (except under
Windows), but the requirement checks can still be done
automatically.

`MANIFEST.in` is used by `setuptools` to tell it what files must
be included when packaging the application.

This will automatically set up a `mousetrap` command that can be
run on the command line through the `entry_points` section of
`setup`.
Added classifiers
Customize the `install` and `egg_info` commands

During `egg_info`, specific dependencies which must be installed
to the system will be checked.  If they are not found, an error
will be written which explains the problem and how it can be fixed
on yum- and apt-based systems.

During `install`, the translations will be compiled so MouseTrap
will be able to detect and use them.
Automatically compile locales on install
Don't display xlib warning for Py3