Closes https://github.com/renovatebot/config-help/issues/275

Rewrites hostRules for increased flexibility. Includes renames of existing fields within a hostRule:
- `endpoint` -> `baseUrl`
- `host` -> `hostName`

Additionally, `domainName` has been added. Migration scripts should take care of these for users but it's recommended to update configs to match the new fields anyway.

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.

Refactors hostRules to use field “hostType” instead of “platform”. hostType can include datasources like npm, maven, pypi, etc.

Closes #2482 

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