valr
Add Ayatana AppIndicator support
This PR introduces support for Ayatana AppIndicator in cbatticon. This enhancement addresses a specific issue where GtkIcon tray apps are not displayed in some scenarios (e.g., with Waybar; see #74 for details).
This PR does not replace GtkIcon but provides the option to choose between Ayatana AppIndicator (enabled with WITH_APPINDICATOR) and GtkIcon through preprocessors. This approach is similar to how LIBNOTIFY is currently handled.
However, there is a known limitation with Ayatana AppIndicator: it does not support click events (see AyatanaIndicators/libayatana-appindicator#4), required for left-click functionality. To work around this, the current implementation take advantage of the fact that a menu is necessary to have an indicator in ayatana, so I decided to use it to display those actions, this as a temporary measure until Ayatana adds support for click events.
