Add goimports to default external tools

addons/externaltools/defaultexternaltoolsrc

 [Global]
-tools=14
+tools=15
 version=1
 
 [Tool 0]
@@ -211,3 +211,18 @@ output=ReplaceCurrentDocument
 reload=false
 save=CurrentDocument
 workingDir=%{Document:Path}
+
+[Tool 14]
+actionName=externaltool_GoImports
+arguments=%{Document:FileName}
+category=Tools
+cmdname=goimports-full-file
+executable=goimports
+icon=text-x-go
+input=
+mimetypes=text/x-go
+name=GoImports Full File
+output=ReplaceCurrentDocument
+reload=false
+save=CurrentDocument
+workingDir=%{Document:Path}