Improve message list item-count display

[brandond]

It would be nice if there was a display of:

1. Total messages in folder vs number of messages found by search filter (if a search is active)
2. Number of messages selected (if any messages are selected)

Item 1 is mostly a convenience request; it's nice to know how many items were searched as well as how many matched the criteria.

Item 2 is more important, as there is no way to know whether you've selected the current page, or all messages, or if some other set of actions resulted in selecting a set of messages that are not visible on the current page.

This has resulted in some amount of user confusion and folks accidentally deleting all messages in a folder when they only intended to delete a single page.