Add Markdown Language Server support

[sebthom]

This PR integrates the https://github.com/microsoft/vscode-markdown-languageserver into Wild Web Developer which enables markdown validation, outline view and refactoring support (e.g. renaming of links and their references). Addresses #1678

Validation:

Rename Support:

Suggestions:

Configuration:

[sebthom]

Same like all the others. it's a bundled npm package.

[mickaelistria]

How is the language server integrated/deployed?

[sebthom]

For path suggestions to work LSP4E needs to be upgraded to a version incorporating this enhancement eclipse-lsp4e/lsp4e#1361

[mickaelistria]

Same like all the others. it's a bundled npm package.

Cool, so automatic IP validation has performed and validated it. Let's merge!