Handle space seperated email adresses in the _to, _cc and _bcc field like seperate addresses.

[intxcc]

See issue: #6457

[alecpl]

Unfortunately there's much more to it. For example:

1. In Elastic skin we have the recipient input widget that should be extended to support space separator.
2. Autocompletion does not work with space delimiter. I.e. if you enter "test@domain.tld " and now you'd start entering an another address it will not autocomplete.

So, my take on this is that we could fix this in Elastic, but for other skins it's more work probably not worth the effort.

[alecpl]

Implemented by 218cd2a.