'r' shortcut additions

[johndoknjas]

• Adds the 'r' shortcut to studies (only requests a computer analysis, doesn't learn from your mistakes since that's not a feature in studies atm).
• For the 'r' shortcut in plain analysis boards, now also opens the computer analysis tab.
• In ui/analyse/src/study/serverEval.ts, removes disabled: root.mainline.length < 5 attr, since from what I can tell the expression is always false at that point.

[ornicar]

I don't want a keyboard shortcut for that.

• It's not an action that should be done so many times.
• Server analysis uses a lot of power and, as such, should not be made too convenient to trigger.