Change "welcome to GitLab" message

Currently, when a user starts a new free GitLab.com account the welcome message is:

Welcome to Gitlab 
Code, test, and deploy together

We should update this message to be more celebratory congratulating them on creating an account and pitch the platform. We could also use similar messaging to the home page.

Faster releases. 
Better code. 
Less pain.
GitLab is a complete DevOps platform. Spend less time on your toolchain and more time on what matters: releasing great software.

ICE score

Impact	Confidence	Effort	Score
2	4	1	2.33