Add a Makefile

This PR adds a Makefile to the project.

Use `make help` to list the targets the Makefile provides:

```shell
$ make help
Usage: make <target>

Possible targets:

- install                 Install c2cgeoform
- initdb                  (Re-)initialize the database
- serve                   Run the dev server
- check                   Check the code with flake8
- modwsgi                 Create files for Apache mod_wsgi
```

For development you will use the `install`, `initdb`, `serve` and `modwsgi` targets.

For production the `modwsgi` target creates an Apache mod_wsgi script (`.build/venv/c2cgeoform.wsgi`) and an Apache mod_wsgi config file (`.builld/apache.conf`).

Things that are missing:

- Set up Travis CI (geoalchemy2 can be used as an example)
- Add a `test` target
- Add an `initdb` target that uses production.ini instead of development.ini?