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/friendly_error.py

@@ -0,0 +1,47 @@
+from typing import Iterable, Optional
+
+
+class FriendlyError(Exception):
+    """
+    An error that is supposed to be shown to the user in a nice format
+
+    Use `raise ... from ...` to preserve context.
+    """
+
+    title_format: str
+    title_args: Iterable[str]
+    subtitle_format: str
+    subtitle_args: Iterable[str]
+
+    @property
+    def title(self) -> str:
+        """Get the gettext translated error title"""
+        return self.title_format.format(self.title_args)
+
+    @property
+    def subtitle(self) -> str:
+        """Get the gettext translated error subtitle"""
+        return self.subtitle_format.format(self.subtitle_args)
+
+    def __init__(
+        self,
+        title: str,
+        subtitle: str,
+        title_args: Optional[Iterable[str]] = None,
+        subtitle_args: Optional[Iterable[str]] = None,
+    ) -> None:
+        """Create a friendly error
+
+        :param str title: The error's title, translatable with gettext
+        :param str subtitle: The error's subtitle, translatable with gettext
+        """
+        super().__init__()
+        if title is not None:
+            self.title_format = title
+        if subtitle is not None:
+            self.subtitle_format = subtitle
+        self.title_args = title_args if title_args else ()
+        self.subtitle_args = subtitle_args if subtitle_args else ()
+
+    def __str__(self) -> str:
+        return f"{self.title} - {self.subtitle}"