Undo changes in `bin/get_bootcamp_info.py`

If run on Windows it will produce the **wrong** answer.
Make `bin/archive_bootcamp_info.py` simpler
Fix bad names in `bin/archive_bootcamp_info.py`
Avoid GitHub rate limit

Wait 60s after remove 20 bootcamps. There is a better way to
avoid GitHub rate limit but since the shell script will be
running only once not worth spend time with it.
Prototype of improvements in cache

This was requested by @gvwilson and is related with 156fbe
(see 3rd step).

Project
-------

After some time (one month) that a bootcamp end its information
will be save in some file (`config/bootcamps_saved.yml`) to make
the build process faster.

Steps
-----

1. Changes in `bin/get_bootcamp_info.py` to archive old bootcamps.
2. Changes in `Makefile` to be compatible with the new feature
   of `bin/get_bootcamp_info.py`.

Status
------

1. Done
2. Done