add legend

[ghost]

add legend using HTML template (#1)

[xhdix]

Thanks for the PR. ❤️ 🌺
Is it possible to have them a bit smaller?
I'm not sure if I did it correctly but:

23,24c23,24
<       width: 270px;
<       height: 360px;
---
>       width: 135px;
>       height: 180px;
228,230c228,230
<       let x = -legend.clientWidth / 2 + 65;
<       let y = -legend.clientHeight / 2 + 30;
<       let step = 70;
---
>       let x = -legend.clientWidth / 2 + 35;
>       let y = -legend.clientHeight / 2 + 15;
>       let step = 35;
236c236
<               x: idx < max_row ? x : x + 125,
---
>               x: idx < max_row ? x : x + 62,
240,241c240,241
<               size: 10,
<               font: '14px arial black',
---
>               size: 5,
>               font: '7px arial black',

[xhdix]

Looks good to me for now.. I'm going to merge it. Thank you @r3xcr4py! ❤️ 🌺

@RYNEQ I will create a new issue for follow-up works and ideas.