frontend: Cockpit should use a custom version of mdi icons on main menu

[ArturoManzoli]

Current behaviour

In some cases, like on 4k resolution with zoom to enlarge, the main menu icons are off-center in relation to the rim around it:

Expected or desired behaviour

The solution would be having a custom svg with the rim already around the icon.

Prerequisites

• I have checked to make sure that a similar request has not already been filed or fixed.