/explore, /write, /sketch: add to bookmarks workflow issues

[andirueckel]

-- Branch: bookmark-feature + develop --

Steps to reproduce the problem

• Navigate to /write and open open one of your pad items.
• Click the add to bookmarks button in the top right corner.

Issues

• The loading spinner needs more width, and leads to visual flickering/movement.
• The check mark emoji, after the loading spinner, needs to be changed to use the check mark icon (svg). 4c9d0f2

Improvements

In addition to these issues, it would be great if the add to bookmarks button would be stateful, i.e. if the item is bookmarked, either disable the button, or replace the button with a remove from bookmarks button with respective icon.