Move the external config file

The server side configuration should have its own file, and not be mixed
in with front-end config. This simplifies the process of figuring out path
by making the only file with fix path we need to include locates in the
same folder as the script.
Now, the user's folder structure is then trivial as we can get to the
config file through __DIR__. For every other files we need to include, we
can read the path to from the config file.
The default config file as a separate file also seems redundant. User is
free to create a backup of the file or come back to the repo to re-download.
There's no clear benefit to loading 2 files and merge the arrays for every
operation.
The config file is also a JSON file and should have the correct
extension.