Added post information for feature toggles to add various features to meilix - (Solves- #400)

[pranav1698]

Checklist

• [x] I have read the Contribution & Best practices Guide and my PR follows them.
• [x] There is a corresponding issue for this pull request.
• [x] My branch is up-to-date with the Upstream master branch.
• [ ] The unit tests pass locally with my changes (provide a screenshot or link for test)
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have added necessary documentation (if appropriate)

Short description of what this resolves:

This adds information for the features toggles, and stores them in a features array This features array is then send to the build server.

Changes proposed in this pull request:

• Adding name, value pair to the feature.
• Storing the name-value pair in a feature array.

Fixes #400

[tabesin]

Please use a more simple naming scheme than "Generator_*" that should then match the environment variables in https://github.com/fossasia/meilix/blob/master/build.sh

[pranav1698]

Ok @tabesin, I am going with FEATURE* for a meilix feature, and PACKAGE* for a package to be installed in the ISO

[pranav1698]

Or we can go with something like SWITCH_ON_* and INSTALL_*

[pranav1698]

@tabesin please review now