Replace AppVeyor with Travis CI for Windows

Fixes #6146

- Removed `appveyor.yml` file
- Replaced the `appveyor.yml` file with new windows sections in the `.travis.yml` file

Signed-off-by: Vincent Fugnitto <vincent.fugnitto@ericsson.com>

.travis.yml

@@ -123,6 +123,7 @@ jobs:
   fast_finish: true
   allow_failures:
     - os: osx
+    - os: windows
   include:
   - stage: test
     os: linux
@@ -131,6 +132,13 @@ jobs:
     before_script: skip
     script:
       - travis_retry yarn test:theia
+  - os: windows
+    env: 
+    - CXX=c++
+    - YARN_GPG=no
+    before_script: skip
+    script:
+      - travis_retry yarn test:theia
   - stage: deploy
     if: NOT type IN (cron, pull_request)
     os: linux

README.md

@@ -11,7 +11,6 @@
   [![PRs Welcome](https://img.shields.io/badge/PRs-welcome-brightgreen.svg?style=flat-curved)](https://github.com/eclipse-theia/theia/labels/help%20wanted)
   [![Spectrum](https://img.shields.io/badge/Chat-on%20Spectrum-blue.svg)](https://spectrum.chat/theia)
   [![Build Status](https://travis-ci.org/eclipse-theia/theia.svg?branch=master)](https://travis-ci.org/eclipse-theia/theia)
-  [![Build status](https://ci.appveyor.com/api/projects/status/02s4d40orokl3njl/branch/master?svg=true)](https://ci.appveyor.com/project/kittaakos/theia/branch/master)
   [![Open questions](https://img.shields.io/badge/Open-questions-blue.svg?style=flat-curved)](https://github.com/eclipse-theia/theia/labels/question)
   [![Open bugs](https://img.shields.io/badge/Open-bugs-red.svg?style=flat-curved)](https://github.com/eclipse-theia/theia/labels/bug)
 
@@ -107,6 +106,6 @@ Read below how to engage with Theia community:
 
 
 ## Trademark
-"Theia" is a trademark of the Eclipse Foundation 
+"Theia" is a trademark of the Eclipse Foundation
 https://www.eclipse.org/theia