VSCode Extension: Bundling and output directory cleanup

[Philipp15b]

This extension consists of 245 files, out of which 186 are JavaScript files. For performance reasons, you should bundle your extension: https://aka.ms/vscode-bundle-extension . You should also exclude unnecessary files by adding them to your .vscodeignore: https://aka.ms/vscode-vscodeignore

Also, the out directory seems not to be cleaned when the extension is built, possibly resulting in (very) old files being included in the extension package.