Made enhancements on buster branch

[d78ui98]

• [x] added auto-config feature
• [x] added feature to set ram and vagrantbox name from settings.sh
• [x] enabled debugging on all bash scripts
• [x] added vagrant-cachier plugin
• [x] added autologin and guest login feature
• [x] improved comments
• [x] added feature to create and destroy vagrant boxes from test.sh

closes #92

[d78ui98]

debhelper version 11 is required to build debian-edu packages. But according to this latest version available for stretch is 10.2.5.

That's why we need to install stretch-backports to get the latest version of debhelper

I referred to the official guide on how to it - https://backports.debian.org/Instructions/#index2h2 and made appropriate changes in edu.sh

we will remove this as soon as education-debian packages that we proposed are merged.