Give the tray an icon a black bar cannot swallow

A session that names no desktop, which is what i3 and a bare X11 login are,
leaves Qt with hicolor as its only icon theme, and hicolor has none of the four
names the tray asks for. So fromTheme returns nothing and the shapes drawn in
trayicon.py are used, as they are on macOS. They were drawn in black, which
macOS recolours through the mask and X11 does not, and i3's bar is black: the
icon was there all along, painted onto a bar of its own colour. Outside macOS
they are now white over a dark copy of themselves spread a pixel out, which
stands out on a dark bar and stays readable on a light one, and the mask is set
only where something reads it.

The .desktop files had the same hole from the other side. They named
audio-input-microphone, which is in Breeze and in Adwaita but not in hicolor, so
the menu entry and the autostart entry were blank on the same systems. install.sh
now draws the application icon into ~/.local/share/icons/hicolor and both entries
name it; uninstall.sh takes it back. The windows carry it too on X11, where a
window has no .desktop file to be looked up in.

Closes #27

install.sh

@@ -16,6 +16,7 @@ PY="$(command -v python3)"
 BIN_DIR="$HOME/.local/bin"
 APP_DIR="$HOME/.local/share/applications"
 AUTOSTART_DIR="$HOME/.config/autostart"
+ICON_DIR="${XDG_DATA_HOME:-$HOME/.local/share}/icons"
 SHORTCUT="${1:-Ctrl+Space}"
 # Without the colon, so that a second argument given as "" stays empty. That is
 # how update.sh says "this one was turned off", as against not saying anything.
@@ -81,7 +82,7 @@ if [[ "${XDG_SESSION_TYPE:-}" != "x11" ]] && command -v ydotool >/dev/null; then
 fi
 
 # 3. Launchers -------------------------------------------------------------
-mkdir -p "$BIN_DIR" "$APP_DIR" "$AUTOSTART_DIR"
+mkdir -p "$BIN_DIR" "$APP_DIR" "$AUTOSTART_DIR" "$ICON_DIR"
 ln -sf "$DIR/dikte.py" "$BIN_DIR/dikte"
 chmod +x "$DIR/dikte.py"
 ok "Command installed: $BIN_DIR/dikte"
@@ -90,13 +91,33 @@ case ":$PATH:" in
   *) warn "$BIN_DIR is not on your PATH. For fish: fish_add_path $BIN_DIR" ;;
 esac
 
+# The icon, drawn by trayicon.py so that there is no binary in the repository,
+# and installed under a name of our own. Naming a theme icon like
+# audio-input-microphone instead only works where a theme has it: on i3 or a
+# bare X11 login Qt is left with hicolor, which has no such name, and the entry
+# comes out blank. hicolor is also where this goes, since it is the theme every
+# desktop must fall back to.
+if "$PY" "$DIR/trayicon.py" --hicolor "$ICON_DIR" >/dev/null 2>&1; then
+  ICON=dikte
+  # Only GTK reads a cache, and only if one is already there; a stale cache
+  # would otherwise hide the file we just wrote.
+  if command -v gtk-update-icon-cache >/dev/null \
+     && [[ -f "$ICON_DIR/hicolor/icon-theme.cache" ]]; then
+    gtk-update-icon-cache -q -f -t "$ICON_DIR/hicolor" 2>/dev/null || true
+  fi
+  ok "Icon installed: $ICON_DIR/hicolor"
+else
+  ICON=audio-input-microphone
+  warn "Could not draw the icon, so the entries name your theme's microphone"
+fi
+
 cat > "$APP_DIR/dikte.desktop" <<EOF
 [Desktop Entry]
 Type=Application
 Name=Dikte
 Comment=Voice dictation: record, transcribe, clean up, paste
 Exec=$PY $DIR/dikte.py
-Icon=audio-input-microphone
+Icon=$ICON
 Categories=Utility;AudioVideo;
 StartupNotify=false
 EOF
@@ -107,7 +128,7 @@ cat > "$AUTOSTART_DIR/dikte.desktop" <<EOF
 Type=Application
 Name=Dikte
 Exec=$PY $DIR/dikte.py
-Icon=audio-input-microphone
+Icon=$ICON
 X-GNOME-Autostart-enabled=true
 StartupNotify=false
 EOF