Launch with defaults instead of not launching upon invalid config/theme

[Omnikar]

If the user tries to start the editor and there is a problem with their config, I think the editor should start with the default config instead of failing to launch. That way, they don't have to use a different editor to fix the problematic config. Likewise, launch with the default theme if their configured theme is problematic. Of course, the editor should issue a warning on startup if either of these situations occur. Also, if the user tries to switch to a problematic theme with :theme, inform them and continue with the current theme instead of panicking.

[Omnikar]

How would we go about displaying the startup error to the user? Statusline message on startup? Or display the message to the user and have them press enter to continue and start the editor? I think the latter, as a problematic theme or config is important enough to require explicit acknowledgement by the user.