ValidationMessages: merge *name-*.invalid

[php-coder]

Likewise we did in #162 but for the following messages:

category-name-en.invalid = Category name must consist only latin letters, hyphen or spaces
category-name-ru.invalid = Category name must consist only Russian letters, hyphen or spaces

country-name-en.invalid = Country name must consist only latin letters, hyphen or spaces
country-name-ru.invalid = Country name must consist only Russian letters, hyphen or spaces