Attempt to make .vimrc errors non-fatal

[Lyude]

Currently we don't have any nice way of handling errors that stem from our .vimrc on start. It's possible that we might be able to add something, but some investigation will need to happen to figure out whether we can either recover from such an error, or maybe even reimplement .vimrc loading ourselves if required for more fine grained error handling.

See #28 for more info

[sdroege]

It's possible that we might be able to add something

The terminal version of nvim handles this fine, so that should definitely be possible one way or another :) I'm just running into this again regularly because some plugin sometimes creates an error during startup and I have not been able to understand yet why (but I know where).