Revert to Configuration::CONSTANT syntax for getting config values

If general.yml and test.yml are present in the config directory, the
config is overridden to use values from those files instead (assumes
that the file lib/themes/hampshire/configuration.rb is present)
Updated README to include a section about overiding the Configuration model
Merge branch 'issues/47-reimplement-config-lib' into hampshire
Add basic markers to the map for the applications on the page

TODO: get the full list, not a paginated one
Allow search_params to be overriden and use per_page from Application
Show all applications Sphinx can return on maps
Limit search distance to 3 miles so that it all fits on the default zoom level