Canvis a "Review notifications"

Ref. PWA11

NOTE: this feature is from a big development. See PWA discussion at GitHub.

Is your feature request related to a problem? Please describe.

As a registered participant who is following content in Decidim, I see many problems with how the current Notifications page is implemented:

• Regarding the date, it just shows the day of the week and day of the month it was sent.
• When there is a new comment, it only shows that “There was a new comment”. For instance, “There is a new comment by Decidim Product @product in Possibility to configure default sorting for proposals.”. It gets linked to the old format (with an anchor link).
• When there is a new proposal it doesn’t show the author. For instance, “The proposal Let admins edit in the backend meetings that they created in the frontend (and vice-versa) has been added to Propose new functionalities for Decidim software”
• When you were mentioned as a group, there’s a bug that won't show which group you were mentioned. For instance, “You have been mentioned in Ability to disable public profiles by Carol Romero @carol as a member of”

I would like these problems not to be.

Describe the solution you’d like

As there are multiple problems we should have multiple solutions:

• Better handling of the date in Notifications (ref. PWA11.1)
• Fix link to comments in Notifications (ref. PWA11.2)
• See the full content of comments in Notifications (ref. PWA11.3)
• Add author to proposals in Notifications (ref. PWA11.4)
• Fix groups mentions in Notifications (ref. PWA11.5)

Describe alternatives you’ve considered

They are all pretty much bugs that we have from the first iteration of notifications, so they’re all pretty straightforward. The only one that there could be more doubts about is regarding showing the full content of comments, as that will mean that we will have different lengths of notifications and could impact the UI/UX.