Rename folder: code => apps

"code" is a vague and indescriptive name for a directory. A better name is
"apps", as the directory contains django applications.

Fix up the readme as necessary to reflect the rename. Also improve some of the
writing in the readme.
Make stylistic changes.

Change double quotes to single quotes. Remove a line, promoting logical grouping
of code.
Remove secret key.

An application's secret key should not be public. This simple and obvious fact is
listed noted in the settings file. Remove it.