Fixed examples for LPP in HEMS and Controlbox

[uhl]

LPP use case shall use negative numbers to show that the stack does not transform positive numbers to negative numbers.

[sthelen-enqs]

This PR also changed the Failsafe Active Production Limit values to be negative.
Failsafe values should always be >= 0

The following values are always greater than or equal to zero. Their name indicates that they are
used for production direction [LPP-010]:

• Failsafe Production Active Power Limit ([LPP-021]): production direction
• Power Production Nominal Max ([LPP-041]): production direction
• Contractual Production Nominal Max ([LPP-042]): production direction

[andig]

Ah, you have to love the specs for consistency.