Update Turkish translation

[Beryesa]

Fix little mistakes and bring it closer to the established translations by the GNOME and KDE Turkish teams for consistency.

[Beryesa]

I should note however that cosmic-library-home doesn't fit (Kitaplık Ana Sayfası)

Should we call it just "Home" (Ana Sayfa) or just "Library" or are there any other plans about longer strings in the UI? :P

[wash2]

Just "Home" would be fine for now. It's a bit awkward to have long names for these buttons. Maybe the text could be made to wrap, and buttons all increase in size to match the largest button height.

[Beryesa]

Hey, just before merging that, I see a string is missing in

cosmic-applibrary/src/app.rs

Line 1187 in d88d0ba

text("Add group")

Should I make another PR for that, or can I extend this one?
Something like text(&fl!("add-group").as_str()) and adding that key to the files helps

Kindly, @wash2

[Beryesa]

Here, #147
I can add it here after that one's merged.

[Beryesa]

Thanks, that was fast! xP
Updated to include it as well.