Specify added/removed spaces on warnings

[pedro-mendonca]

Use _n() to specify both added and removed spaces on warnings about different spacing at the beginning or ending of translation strings.

Current:

The translation appears to be adding one or more spaces at the beginning.
The translation appears to be adding one or more spaces at the end.
The translation appears to be missing one or more spaces at the beginning.
The translation appears to be missing one or more spaces at the end.

Suggestion:

Related to #1427

[NekoJonez]

Speaking about the spaces at the end and such... In WPGP by @vlad-timotei, it also shows that. It also gives you a warning for double spaces. But, that's something we in nl_NL/nl_BE ignore because grammar... So, maybe add a feature to ignore double spaces and make it fine for one space?