Helpers: add get env function

Signed-off-by: Vasiliy Doylov <nekocwd@mainlining.org>

src/logic/helpers.vala

@@ -8,4 +8,10 @@ namespace EyeNeko {
             return ((EnumClass) Type.from_name (enum).class_peek ()).get_value (value).value_name;
         }
     }
+    namespace Env {
+        string get_variable_or (string name, string default) {
+            var str = Environment.get_variable (name);
+            return (str == null ? default : str);
+        }
+    }
 }