Improvements to the chat links system

[Ellypse]

The new chat links system could be improved in several ways, to be more robust, offer better user feedback and use fewer resources:

• [x] Generate tooltip content on link creation and save it in a table once, instead of calling function to generate tooltip text for each request
• [x] Save raw content to send once instead of fetching for each request
• [x] Compress data sent
• [x] Compute the size of the data when sending the first link info and have the size of the thing being send indicated in the tooltip
• [x] Add a loading indicator to the tooltip when it is first fetching the tooltip data
• [x] Add a loading bar (or indicator if a bar is not possible or too hard to do) to the tooltip when using an action button like opening or importing something.