Reformat and reformulate 2x2 buttons

• Reformat buttons such that they don't wobble so much between 1/2/3 line formats (by introducing larger max-width and minimum height)
• Reformulate buttons to same names as in Hamburger menu, where applicable
• Exchange links for education hamburger menu <> buttons, as of comment in #274
• Since principally all links of these 2x2 buttons are external, don't add explicit "external" symbol there. Is that appropriate?

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