Added a feature to save logs to local storage (#1741)

- Added export logs to local storage
[1664](https://github.com/tiann/KernelSU/issues/1664)

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Co-authored-by: weishu <twsxtd@gmail.com>

manager/app/src/main/res/values/strings.xml

@@ -130,4 +130,5 @@
     <string name="flash_success">Flash success</string>
     <string name="flash_failed">Flash failed</string>
     <string name="selected_lkm">Selected lkm: %s</string>
+    <string name="save_log">Save Logs</string>
 </resources>