Upgrade dependencies to fix security vulnerabilities (2.x)

[bajtos]

• Simplify build (backport #435):
  • Remove e2e tests that are no longer runnable anyways
  • Remove dependency on karma, phantomjs and browserify, they were needed for e2e tests only
  • Replace Grunt with npm scripts
• Upgrade jayson from 1.x to 2.x (backport #442)
• Update deps to fix security vulnerabilities
• Travis: enable Node.js 10.x

This fix is needed to make npm test in loopback-workspace pass again. Right now, applications scaffolded for LB 2.x are failing their npm test because of security vulnerabilities reported by nsp check.

[bajtos]

Please note that the latest versions of jscs & jshint are depending on a lodash version that's vulnerable to Prototype Pollution. Since these are dev-dependencies, I think we don't need to worry.

If we wanted to fix the problem, we would have to migrate from jshint+jscs to eslint+eslint-config-loopback.