tests: remove DownloadedDatasetTestCase

Since this TestCase sub-class merely set a constant, it seems more
idiomatic to have, well, a constant. Fix up uses of
DownloadedDatasetTestCase elsewhere.
api: expose expected tile resolution in app config

Add a new configuration parameter, ELEVATION_TILE_RESOLUTION, which can
be used to configure the expected tile resolution. Required for the test
suite in which the mock dataset has a different resolution.
tests: add test for web api

Using the wonderful Flask-Testing package, exercise the web API a little
checking for failure modes and that it gives outputs consistent with
calling Dataset.get() directly. The calls to Dataset.get() are
indirectly tested via the ASCII art maps test.
README: add travis/coveralls badges

We're not a cool project unless we have these in our README.
api: use flask-script for development server

The "idiomatic" way to have a ``ruaumoko-api``-like tool with flask is
to use Flask-Script's manager object. For one line of code, we get the
same support which we previously had along with the ability to specify
bind address and port which is occasionally useful. It also supports
live-reloading of the Python module which is almost always useful for
development.
manager: add configuration from environment

For the development web server the environment variable
``RUAUMOKO_SETTINGS`` may now optionally be set. If it is set, it points
to a configuration file which can be used to configure the webapp
settings including, but not limited to, the path to the ruaumoko
dataset.
manager: add copyright banner

Add copyright banner which should be atop all source files.
Merge pull request #25 from rjw57/use-flask-script

make the development webserver useful for development
README: add PyPI badges
Merge pull request #23 from rjw57/test-api

add tests for the web API
README: add note on how to enable debugging
Merge pull request #26 from rjw57/readme-add-note-on-debugging

README: add note on how to enable debugging
Merge pull request #24 from rjw57/add-badges

README: add travis/coveralls badges
setup: add GDAL dependency

GDAL is a library which allows direct access to a variety of Geospatial
Data formats. (It is, in fact, a Geospatial Dataset Abstraction
Library.)

The Python bindings are distributed separately on PyPI as the GDAL egg.
Add it as a requirement to setup.py.
travis: add GDAL setup magic

On the 12.04 Ubuntu boxes which act as Travis workers, the distro GDAL
packages are quite old so add the ubuntugis PPA to enable a more modern
GDAL to be installed. Also specify the exact version of the Python
bindings to install in order to match the installed GDAL.
download: read dataset information via GDAL