Better error reporting when publishing

[Andersama]

Currently if a page fails to be generated while publishing the whole process fails silently. Instead, display some form of checklist of successfully generated pages vs ones with errors. Also works as visual feedback that there is something happening when publishing.

Edit: The main benefit being it also helps point users to which pages are preventing publishing from occurring.

[Andersama]

Going through the codebase to make sense of how it works. I think compile_component_head and block_html and a couple other functions appear to be discarding errors. There's a lot of try catch error handling in the code, but I think the better approach here is to collect errors into your own list, and then when "compilation" completes check that there aren't any*, but also if there are display them to the user.

If preview / download is selected that same list could be made into a popup to display which pages failed/rendered ok.