Implement Tray Icons

This commit implements the StatusNotifierItem protocol, and enables
swaybar to show tray icons. It also uses `xembedsniproxy` in order to
communicate with xembed applications.
The tray is completely optional, and can be disabled on compile time
with the `enable-tray` option. Or on runtime with the bar config option
`tray_output none`.

Overview of changes:
In swaybar very little is changed outside the tray subfolder except
that all events are now polled in `event_loop.c`, this creates no
functional difference.

Six bar configuration options were added, these are detailed in
sway-bar(5)

The tray subfolder is where all protocol implementation takes place and
is organised as follows:

tray/sni_watcher.c:
	This file contains the StatusNotifierWatcher. It keeps track of
	items and hosts and reports when they come or go.
tray/tray.c
	This file contains the StatusNotifierHost. It keeps track of
	sway's version of the items and represents the tray itself.
tray/sni.c
	This file contains the StatusNotifierItem struct and all
	communication with individual items.
tray/icon.c
	This file implements the icon theme protocol. It allows for
	finding icons by name, rather than by pixmap.
tray/dbus.c
	This file allows for asynchronous DBus communication.

See #986 #343

1 files changed, 36 insertions, 0 deletions

diff --git a/sway/sway-bar.5.txt b/sway/sway-bar.5.txt
index 5a52e7db..29487662 100644
--- a/sway/sway-bar.5.txt
+++ b/sway/sway-bar.5.txt
@@ -65,6 +65,42 @@ Commands
 **height** <height>::
         Sets the height of the bar. Default height will match the font size.
 
+Tray
+----
+
+Swaybar provides a system tray where programs such as NetworkManager, VLC,
+Pidgin, etc. can place little icons. The following commands configure
+interaction with the tray or individual icons.
+The _button_ argument in all following commands is a Linux input event code as
+defined in linux/input-event-codes.h. This is because wayland defines button
+codes in this manner.
+
+**activate_button** <button>::
+        Sets the button to be used for the _activate_ (primary click) tray item
+        event. By default is BTN_LEFT (0x110).
+
+**context_button** <button>::
+        Sets the button to be used for the _context menu_ (right click) tray item
+        event. By default is BTN_RIGHT (0x111).
+
+**secondary_button** <button>::
+        Sets the button to be used for the _secondary_ (middle click) tray item
+        event. By default is BTN_MIDDLE (0x112).
+
+**tray_output** none|all|<name>::
+        Sets the output that the tray will appear on or none. Unlike i3bar, swaybar
+        should be able to show icons on any number of bars and outputs without
+        races. Because of this, the default value for this is _all_.
+
+**tray_padding** <px> [px]::
+        Sets the pixel padding of the system tray. This padding will surround the
+        tray on all sides and between each item. The default value for _px_ is 2.
+
+**icon_theme** <name>::
+        Sets the icon theme that sway will look for item icons in. This option has
+        no default value, because sway will always default to the fallback theme,
+        hicolor.
+
 Colors
 ------