Improve look of priority inbox

[nimishavijay]

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

The priority inbox is the first thing we see when we open the Mail app, some design improvements could go a long way to make the Mail app more polished.

Describe the solution you'd like

@jancborchardt and I worked on making some design changes that (hopefully) make the experience better.

New priority inbox	Skeleton screen	No important mails

Major changes:

• Remove the "Favorite" section as it can be accessed from the navigation
• Move the "New message" and "Refresh" button from top of navigation to top of the mail list Redesign the second column #6774
• Instead of "Important and unread" show only all important mails (read and unread) as you can't access the important mails from anywhere -- what do you think? Many email clients allow different configurations of the inbox so it's not clear which is the most common one.
• Show more emails in the Important section --> if possible we could calculate the maximum number of mails that can be shown from the height of the viewport?
• Show skeleton screen while loading instead of the loading spinner
• Hide Important section when it's empty
• Show skeleton for the thread details. There shall be placeholders for the title, sender etc of a typical thread and one message

Minor changes:

• - Change refresh icon to MDI refresh
• - Left align the message shown when a section is empty
• - Also change the text so that it is more helpful when there are no important mails
• "No messages" --> "Messages marked as important will show up here"
• - Add icon and change alignment of "Load more"

What do you think?
cc @jancborchardt and @karlitschek

Describe alternatives you've considered

No response

Additional context

(edit: decided with Jan that the collapsing of the important section is not necessary after all, and changed the screenshots to reflect that)

[thstyl2000]

You're doing a great work, but I've got to be honest: I haven't yet found a way to include 'Important' messages to my workflow....
I am personally using a tagging/folder system for my work account and a favorites/folder system for my personal email.

From this point of view, how about having no 'Imprtant' list, but only favorites, but the important emails get sorted on top?