Implement search provider (#201)

* Begin work on search provider

* Initial search provider work, organize meson

* Initial work on icons

* Implement LaunchSearch

* Don't hold arbitrary reference to service

I don't know why Lollypop does this

* Send notification, pad images

* Update translations

* Fix init_search_term typing

cartridges/errors/error_producer.py

@@ -0,0 +1,28 @@
+from threading import Lock
+
+
+class ErrorProducer:
+    """
+    A mixin for objects that produce errors.
+
+    Specifies the report_error and collect_errors methods in a thread-safe manner.
+    """
+
+    errors: list[Exception]
+    errors_lock: Lock
+
+    def __init__(self) -> None:
+        self.errors = []
+        self.errors_lock = Lock()
+
+    def report_error(self, error: Exception) -> None:
+        """Report an error"""
+        with self.errors_lock:
+            self.errors.append(error)
+
+    def collect_errors(self) -> list[Exception]:
+        """Collect and remove the errors produced by the object"""
+        with self.errors_lock:
+            errors = self.errors.copy()
+            self.errors.clear()
+        return errors