Updated Hebrew translation
Add folder progress monitor, hook it up to spinner

This adds a progress monitor to the folder open operation.  The spinner
in the status bar is hooked up to it only for the currently selected
folder, so that background updates don't trigger the spinner.

Closes: bgo #713703
Pluralize tooltips with multiple selection

Looks like when we went to the pill toolbar, we lost our plural tooltips
on the toolbar.  This hooks up to the tooltip changed signal to keep the
buttons in line with the action, which we're setting from the
controller.

Closes: bgo #720710
Updated Polish translation
Round displayed received time to nearest hour

Closes: bgo #720843
Updated Czech translation
Add "use imap credentials" option to "other" acct

This adds a "use imap credentials" checkbox to the "other" account
creation dialog.

Closes: bgo #721964
Merge branch 'master' into wip/unread-status-714865