feat(app,android): a new icon, and a launcher label that fits

The icon follows proton-drive-linux's logo: a violet gradient tile with
a darker lower edge, and a white play mark with a soft shadow, cut into
the blocks a revision is fetched in. The SVG, the window PNG and the
Windows .ico are rendered from one source.

On Android it is an adaptive icon with a monochrome layer for themed
icons, and the notification glyph is the same mark. The app is named
"Proton Stream"; the launcher shows "Stream", since "proton-stream" was
cut to "proton-st…".

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

@@ -1,3 +1,9 @@
 <resources>
-    <string name="app_name">proton-stream</string>
+    <!-- Settings, recents, notifications and the share sheet: room for the full name. -->
+    <string name="app_name">Proton Stream</string>
+    <!--
+      Under the launcher icon, where about ten characters fit before the
+      launcher cuts the label off; "proton-stream" showed as "proton-st…".
+    -->
+    <string name="launcher_name">Stream</string>
 </resources>