Added several fixes to UX and functionality for recent text editors - e.g. copy paste online image feature to rich text editor

- Added copy paste online image feature to rich text editor
- Add auth to image upload option to prevent non-authenticated users from uploading images
- Move close button of image upload modal at top-right corner of modal, and added close modal clickability to modal background
- Fixed minor issues of mobile responsiveness for /compose and /write page
- Fixed bug where toggle state is messed up if one accesses /write or /compose URLs directly.