travis: parallelize evaluation and limit RAM usage

The new test runner will evaluate all test profiles from the README.md
in parallel in separate nix-build processes.
Since we do not load all processes into one process,
this also helps saving memory.

Adding Dell XPS 15 9560

1 default one, with nvidia working and intel working, needs optirun to
run application with nvidia
2 intel only, I am using this as my daily driver for long time, only
intel is turned on and nvidia is turned off and doesn't drain any
power.
3 nvidia only, intel is dissabled and nvidia is picked as default gpu,
no need to fiddle with optirun etc, good for gpu heavy application.

All these settings needs to reboot to work properly

Virtual console options were renamed in 20.03; use `console.earlySetup`
or `boot.earlyVconsoleSetup` depending on OS version.

https://github.com/NixOS/nixos-hardware/pull/114#discussion_r374953204

xps/15-7590: don't enable unfree firmware by default

thinkpad/e495: fix evaluation

fixes #145

Added profile for issues 69289

Co-Authored-By: Jörg Thalheim <Mic92@users.noreply.github.com>

Add Lenovo ThinkPad L13 profile

Add Dell XPS 15-7590 suggested options

Also don't set nixpkgs.pkgs. Instead just add an overlay.

These suggested options are taken from my configuration but aren't quite
universal enough to be enabled by default.

This reverts commit 77983d16.

apparently github can link to wiki text fine.

This allows it to symlink it in the README

Initial 15-7590

Co-Authored-By: Jörg Thalheim <Mic92@users.noreply.github.com>

Add Lenovo ThinkPad X280 profile

dell/xps: enable thermald service

Replace ad hoc throttling fix with throttled