Support for mobile device and network speed emulation

[ayushchatur]

What:

1. Disintegration of core engine to segregate launching and emulation utils
2. Support for emulation of mobile device and network to be taken from config.js
3. Added support for puppeeter .

Why: For supporting Support for mobile device and network speed emulation

How:

1. exploitation of emulation form factor for desktop and tablet/device emulation via passing UAString to the chrome flags
2. creation of net throttling object wrt. lighthouse network mode JSON object

Checklist:

• [ x] Documentation
• [ ] Tests
• [ x] Ready to be merged
• [ x] Added myself to contributors table