feat!: implement Application API

src/icon_theme.rs

@@ -0,0 +1,20 @@
+// Copyright 2023 System76 <info@system76.com>
+// SPDX-License-Identifier: MPL-2.0
+
+use std::cell::RefCell;
+
+thread_local! {
+    /// The fallback icon theme to search if no icon theme was specified.
+    pub(crate) static DEFAULT: RefCell<String> = RefCell::new(String::from("Pop"));
+}
+
+/// The fallback icon theme to search if no icon theme was specified.
+#[must_use]
+pub fn default() -> String {
+    DEFAULT.with(|f| f.borrow().clone())
+}
+
+/// Set the fallback icon theme to search when loading system icons.
+pub fn set_default(name: impl Into<String>) {
+    DEFAULT.with(|f| *f.borrow_mut() = name.into());
+}