Add `CodeArea` to Wirecloud

Proposed changes

Adds a CodeArea styled element that is a full-fledged code editor supporting syntax highlighting of many languages and code completion of a few. Additionally, this allows the use of CodeArea as a preference type for widgets/operators (allowing to specify the language) as well as TextArea.

For this to be possible, the monaco editor has been used (MIT License), which is the same that VS Code uses (it is extracted from its source code). In case monaco fails to load, the CodeArea will be a simple TextArea.

Types of changes

What types of changes does your code introduce to the project:

[ ] Bugfix (non-breaking change which fixes an issue)
[x] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

[x] I have read the CONTRIBUTING doc
[x] I have signed the CLA
[x] I have added tests that prove my fix is effective or that my feature works
[x] I have added necessary documentation
[x] Any dependent changes have been merged and published in downstream modules

Further comments

For monaco to be loaded, webpack has been used. A script was created so that a single command (docs in README) can build monaco and prepare it for Wirecloud.

~This is still a work in progress, as tests are still missing.~ This is ready for review.

Happy coding!

Wirecloud / wirecloud