Elastic: improve extensability of hover menu

[johndoh]

I know I could do this with a plugin and the skin-message-list-hover-menu-init and skin-message-list-hover-menu hooks but the only visible effect of this change is to swap the delete and flag icons around (so that hover menu, or no hover menu, the flag stays in one place).

with these changes then using only custom styling in _styles.less its possible to customise the menu quite a lot more than currently.

1. adding flagged/deleted class to the menu - allows for the text colour to change like it does on the row itself to reflect the status of the message
2. having both the date and size text spans populated allows both bits of information to be displayed if required

in the example above the date is no longer obscured during hover and both the date and size are visible

[johndoh]

The failing coding style check is not related to this PR