Use minority language's flags

Hi,

there are complaints in the growing Basque speaking Linux Mint community about the use of the Spanish/French flags in the login screen.

I found that there are some flags that can be used for minority languages in this repository in the folder mint-mdm-themes-html/usr/share/mdm/html-themes/common/img/languages/, so I thought why don't we use them? I think that many people would feel more comfortable that way.

Catalan (ca) -> "_Catalonia.png"
Welsh (cy) -> "_Wales.png"
Basque (eu) -> "_Basque Country.png"
Scottish Gaelic (gd) -> "_Scotland.png" 
Galician (gl) -> "_Galicia.png"
Scots (sco) -> "_Scotland.png"

Best regards