Implement authentication

• By opening this merge request, you agree to release your code and all other changes under the GPL 3 license and to abide by the terms set by this license.

• Significant changes of this merge request have been added to the changelog.

• Security audit.

• Stress testing. Handles 100+ logins per second and 10+ registrations per second.

• Playtesting.

• Signup page testing in different browsers.

• Add note on the main menu that details how to create an account.

• do name case insensitivity for the register check

Signup page: https://account.veloren.net