With Renovate’s github platform code now using git for all file system operations, we need to tell Renovate which gitAuthor to use.

If you had already configured a gitAuthor in your bot config, you do not need to make any change.

Otherwise, to keep functionality as before, you should either:
(1) configure `gitAuthor` to match the bot’s account, or
(2) recreate your bot’s personal access token to include the “user:email” permission so that the bot can retrieve the email itself

BREAKING CHANGE: GitHub bot admins should either configure gitAuthor in their config or generate a new token with “user:email” permissions.

Rename all VSTS references to be Azure DevOps.

Closes #2810

BREAKING CHANGE: 'vsts' platform is now renamed to 'azure'

Adds platform support for Bitbucket cloud.

Closes #136, Closes #2238

This PR adds support for Microsoft's [Visual Studio Team Services](https://www.visualstudio.com/team-services/) platform (in addition to existing GitHub and GitLab support). 

Closes #571 

Refactors file system of platforms and adds test to ensure GitHub and GitLab have same module.exports signatures.