Update README, LICENSE and CHANGELOG + add dependabot

[theoludwig]

What is the purpose of this pull request? (put an "X" next to item)

• Documentation update
• Bug fix
• New feature
• Other, please explain: Add .github/dependabot.yml

What changes did you make? (Give an overview)

• Update README.md (with badges like travis build passing, ts-standard etc.)
• Update LICENSE to have a "official" MIT License, currently we have a MIT LICENSE from the vscode-eslint fork, but it is not recognized by github as a LICENSE
• Add .editorconfig (same config as standard repo)
• Add .github/dependabot.yml

Which issue (if any) does this pull request address?

As discussed there : #131

Is there anything you'd like reviewers to focus on?

I don't know why the number of changes are so large, I deleted this comment in both client/src/extension.ts and server/src/server.ts :

/* --------------------------------------------------------------------------------------------
 * Copyright (c) Microsoft Corporation. All rights reserved.
 * Licensed under the MIT License. See License.txt in the project root for license information.
 * ------------------------------------------------------------------------------------------ */

I did nothing else in these files but git is still showing a large number of changes since b99d8ad.

We should remove the stale branches from the old Greenkeeper bot https://github.com/standard/vscode-standardjs/tree/greenkeeper/initial once this has been merged.

[feross]

We need to preserve the existing license text, perhaps in a file called ThirdPartyNotices.txt like Microsoft has done. We can't just remove that info. I'll add that in a followup commit.