PLT-4404/PLT-4578/PLT-4541/PLT-4542 Replaced third party autosizing textarea with a custom one (#4442)

* PLT-4578 Replaced third party autosizing textarea with a custom one

* Fix Textbox.handleHeightChange not being called

* Removed unused CSS

* PLT-4541 Force EditPostModal to resize upon opening

* Removed usage of jquery from AutosizeTextarea

* Reverted changes made for PLT-4580 as they're no longer needed

webapp/package.json

@@ -24,7 +24,6 @@
     "perfect-scrollbar": "0.6.12",
     "react": "15.3.2",
     "react-addons-pure-render-mixin": "15.3.2",
-    "react-autosize-textarea": "0.3.3",
     "react-bootstrap": "0.30.3",
     "react-custom-scrollbars": "4.0.0",
     "react-dom": "15.3.2",