Enhance traybar icons (#857)

* add new icons (with border and filled), remove macos for light theme

* remove dark mode detection (it was not working)

* remove build tag and use file suffix for conditional build

* Use `SetIconTemplate`, this allows theme switching on macos

* partially revert 0444f2a

Macos needs transparent icon to apply templating

* rework icons:

 macos icons have been re-exported (to the correct size/color/opacity)
 windows icons have been re-exported from the linux ones (with the border)

 added also two svg files that should allow working on the icon easier in the future

Author: umbynos

icon/icon.svg

@@ -0,0 +1,23 @@
+package icon
+
+import _ "embed" // import embed to embed the icon
+
+// GetIcon will return the icon
+func GetIcon() []byte {
+	return data
+}
+
+// GetIconHiber will return the hibernated icon
+func GetIconHiber() []byte {
+	return dataHibernate
+}
+
+// data represents the icon
+//
+//go:embed icon_mac.png
+var data []byte
+
+// dataHibernate represents the icon hibernated
+//
+//go:embed icon_mac_hiber.png
+var dataHibernate []byte