Simplify how data is passed to Long term graph

[rdwebdesign]

What does this PR aim to accomplish?

• Simplify how data is passed to Long term graph

How does this PR accomplish the above?

• Remove unnecessary step used to fill all empty time-slots with zeros.
• Set the min and max for the x-axis on javascript code and let chartsj handle the empty slots.

What documentation changes (if any) are needed to support this PR?

none

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[PromoFaux]

Discussion here: #2372

[rdwebdesign]

Note:
I rebased the branch.

[yubiuser]

Works with my fake data.

[yubiuser]

Confirmed working in #2372

[yubiuser]

We might need to revise

Remove unnecessary step used to fill all empty time-slots with zeros.

as spanGaps: false isn't going to work anymore.

Instead of adding 0 we could add NaN and get a real break like here: https://jsfiddle.net/srq8hzw2/

[yubiuser]

Setting it to NaN

[yubiuser]

The code will need adjustment - it now prints nothing if not both datasets (blocked, permitted) contain data. If only one contains data, the other isn't shown for that interval.

[rdwebdesign]

I think I fixed.

Please, test the new branch.
If it works, I'll open a PR.