Change webui directory structure and update build scripts

[zelfroster]

The directory structure and names were a bit confusing. So, I have tried to fix it and a few more stuff as well.

This PR has dependency on the changes made in libretroshare. I will raise a PR with the necessary fixes soon.

I have tested the build scripts for linux, windows build script might need test (I think it will be working well as the changes were minor)

Old Structure

RSNewWebUI
├── data
│   ├── retroshare.svg
│   └── user.svg
└── webui-src
    ├── assets
    │   └── index.html
    └── styles
        └── app.css

New Structure

RSNewWebUI
└── webui-src
    ├── assets
    │   └── images
    │       ├── retroshare.svg
    │       └── user.svg
    ├── index.html
    └── styles.css

Changes

• Moved index.html and app.css(renamed to styles.css) to root webui-src directory, (Since, CSS files will be always build and minified into a single file, so there was no need for a directory for app.css).
• Moved assets from data/ directory to webui-src/assets directory (since the assets were images, so created a new images/ directory for them)
• Updated and Improved the build scripts and webui.pro file to include all the necessary files correctly in the output.'
• Removed Old and Unused Files. (GSoC_2019.txt, TODO.md, chat.css and main.css in make-src dir)
• Removed tests directory as I don't think it is used.
• Updated make-src/README