NeovimConnector::spawn now accepts nvim parameters

- When calling spawn to launch a Neovim process we may want to append
  additional parameters to the command line
Fix connection to QLocalSocket:error
Rename Neovim::neovimEvent as neovimNotification
Ignore function attribute deferred
UTF8 fallback for encode/decode with no connection

- Add qWarning message when encoding/decoding before the connection
  is established
- Fallback to utf8
Pass neovim ::spawn() parameters at the begining

- When spawning Neovim with command line parameters, pass the given
  parameters first, and --embed at the end