Add features to add flatpak apps on linux (#161)

* Add features to add flatpak apps on linux

* Fix build on windows

src/flatpak/mod.rs

@@ -0,0 +1,5 @@
+mod platform;
+mod settings;
+
+pub use platform::*;
+pub use settings::*;

src/flatpak/platform.rs

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+use serde::{Deserialize, Serialize};
+
+use crate::platform::{Platform, SettingsValidity};
+use std::error::Error;
+
+use super::FlatpakSettings;
+use steam_shortcuts_util::{shortcut::ShortcutOwned, Shortcut};
+
+#[derive(Debug, Deserialize, Serialize, Clone)]
+pub struct FlatpakPlatform {
+    pub settings: FlatpakSettings,
+}
+
+#[derive(Debug, Clone)]
+pub struct FlatpakApp {
+    pub name: String,
+    pub id: String,
+}
+
+impl From<FlatpakApp> for ShortcutOwned {
+    fn from(app: FlatpakApp) -> Self {
+        let launch_parameter = format!("run {}", app.id);
+        Shortcut::new("0", &app.name, "flatpak", "", "", "", &launch_parameter).to_owned()
+    }
+}
+
+impl Platform<FlatpakApp, Box<dyn Error>> for FlatpakPlatform {
+    fn enabled(&self) -> bool {
+        self.settings.enabled
+    }
+
+    fn name(&self) -> &str {
+        "Flatpak"
+    }
+
+    fn get_shortcuts(&self) -> Result<Vec<FlatpakApp>, Box<dyn Error>> {
+        use std::process::Command;
+        let mut command = Command::new("flatpak");
+        let output = command
+            .arg("list")
+            .arg("--app")
+            .arg("--columns=name,application")
+            .output()?;
+        let output_string = String::from_utf8_lossy(&output.stdout).to_string();
+        let mut result = vec![];
+        for line in output_string.lines() {
+            let mut split = line.split("\t");
+            if let Some(name) = split.next() {
+                if let Some(id) = split.next() {
+                    result.push(FlatpakApp {
+                        name: name.to_string(),
+                        id: id.to_string(),
+                    })
+                }
+            }
+        }
+        Ok(result)
+    }
+
+    fn settings_valid(&self) -> crate::platform::SettingsValidity {
+        let shortcuts_res = self.get_shortcuts();
+        match shortcuts_res {
+            Ok(_) => SettingsValidity::Valid,
+            Err(err) => SettingsValidity::Invalid {
+                reason: format!("{}", err),
+            },
+        }
+    }
+
+    #[cfg(target_family = "unix")]
+    fn create_symlinks(&self) -> bool {
+        false
+    }
+
+    fn needs_proton(&self, _input: &FlatpakApp) -> bool {
+        false
+    }
+}

src/flatpak/settings.rs

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+use serde::{Deserialize, Serialize};
+
+#[derive(Debug, Deserialize, Serialize, Clone)]
+pub struct FlatpakSettings {
+    pub enabled: bool,
+}