SwayTaskbar module: support for "reverse DNS"-style .desktop file names
On panel startup, all the "reverse DNS"-style named .desktop files are being mapped to icon names found inside. The SwayTaskbar module first tries to create the task icon on the basis of app_id or wm_class value. If no icon found in GTK theme, the desktop-file-name-to-icon dictionary will be searched. If name found in keys, the assigned icon will be used. This closes #64.
NOTE: looking for the Icon= definition in .desktop files is a fallback method, which increases resources usage. Use icon themes that provide as many properly named application icons as possible.