Support for plugin contribution property command#shortTitle and menu#group

[jonah-iden]

Feature Description:

When going to file->New File... a file type picker opens. Vscode uses some information for this file picker currently not available in Theia.

Vscodes file picker looks like this:

For the QuickPickItem.label, vscode uses the shortTiltle property from the command as seen here in the python extension:

Entries are also grouped by the group property from the MenuNode contribution as seen here in the built-in ipynb extension

Also the extension name from the command should be used for the QuickPickItem.description

These properties should also be used for theias new file type picker.