Reorganize .gitignore: (#16925)

- group entries
- remove duplicate ".idea" entry
- ignore npm@5 package-lock.json

.gitignore

@@ -12,7 +12,6 @@
 *.map
 *.swp
 .DS_Store
-npm-debug.log
 
 _Resharper.DefinitelyTyped
 bin
@@ -25,20 +24,28 @@ Properties
 # test folder
 _infrastructure/tests/build
 
+# IntelliJ based IDEs
 .idea
 *.iml
+
 *.js.map
 !*.js/
 !scripts/new-package.js
 !scripts/not-needed.js
 !scripts/lint.js
 
+# npm
 node_modules
+package-lock.json
+npm-debug.log
 
+# Sublime
 .sublimets
-.settings/launch.json
 
+# Visual Studio Code
+.settings/launch.json
 .vs
 .vscode
+
+# yarn
 yarn.lock
-.idea