Linux - Replace legacy desktop integration with modern XDG-based integration

Replace manual placement of .desktop files with modern XDG-based install process.

Update .desktop file to leverage modern XDG functions (namely, the ability for an application to request to be ran on the system's most powerful GPU, useful for hybrid graphics setups).

Also provides provisions for launching the viewer on the iGPU and associating SLURLs via the desktop file, accessible by right-clicking the desktop shortcut.

indra/newview/linux_tools/refresh_desktop_app_entry.sh

@@ -45,7 +45,7 @@ PrefersNonDefaultGPU=false
 [Desktop Action AssociateMIME]
 Exec=${installation_prefix}/etc/register_secondlifeprotocol.sh
 Name=Associate SLURLs
-Comment=Set this viewer as the default handler for secondlife:// links.
+Comment=Set this viewer as the default handler for secondlife:// and hop:// links.
 desktopfile
 
 #The above adds some options when the shortcut is right-clicked, to launch on the default (usually integrated) GPU, and to force MIME type association.