Support serve-d's non-standard LSP extensions

[WebFreak001]

Currently the non-standard extensions which the editor may optionally implement (documented in README starting with coded/) include:

• HTTP downloader for serve-d to download DCD with UI (just aesthetics)
• dedicated installation output log UI
• DUB dependency & package info tree
• project DUB build, config, arch & compiler settings in toolbar
• DUB build system integration (build tasks)
• unittesting integration (run/debug single, module, project + list with goto; upcoming)

[aminya]

This can be a very good showcase for the atom-vscode project:
https://github.com/atom-community/atom-vscode