Download all missing custom nodes

[AI-taja]

A lot of the times when using the manager for clean installs of Comfy, I need to install each custom node separately.
A button that just installs all of them at once would be really useful.

[ltdrdata]

1. goto missing node dialog
2. check one of them
3. select all checkbox
4. click install button

It will install all selected nodes.

FYI, a UX upgrade PR is currently in progress, so this behavior will change.
#744