cmd/geth: added 'geth bug' command (#3684)

* cmd/geth: added 'geth bug' command

Added bug command to geth, which will open a browser window
with an issue template and some additional system information.

* cmd/geth: update bug with better infos

* cmd/geth: added browser fallback

* cmd/geth: govet yo momma

cmd/geth/main.go

@@ -81,6 +81,7 @@ func init() {
 		// See misccmd.go:
 		makedagCommand,
 		versionCommand,
+		bugCommand,
 		licenseCommand,
 	}