Add justify config option for Labels

[dann-merlin]

This is PR adds the option to specify a "justify" field for aligning text modules. It should be either "left", "right" or "center".

This is especially useful for centering the text in labels on vertical bars. In situations like this:

"format": "{icon}\n{value}%",
This kind of fix was already mentioned in #366, however it was never implemented, so here's my take on it.

An example config for this:

    "memory": {
        "format": "\n{}%", // That's a character for a RAM module in the font I'm using.
        "justify": "center",
    },

[Alexays]

Nice, can you add this to the man and github wiki?

[dann-merlin]

This would need to be added to basically all module documentations, right?

[twohexed]

Would love to see this implemented, I myself have been wanting this!

[Alexays]

Sorry for the delay, yep should be added to all modules that inherit label class :)

[machitgarha]

So all we need is documentation for this to get merged?

[dann-merlin]

Alright, I've added documentation for justify whereever I was able to find documentation for align. Which should be everything that inherits the label class.
I also slightly changed the documentation for align, in order to clarify the difference between these two options.

Let me know if there's anything else!

[Alexays]

LGTM, thx!