Upgrade to most recent version of Leaflet

[amotl]

Hi there,

currently, this repository includes Leaflet 1.3.1 on behalf of the src/libs/leaflet.js file. However, it should be better included by adding it as a runtime dependency into package.json.

Within #78, we are looking at integrating Leaflet-Geoman and I believe it will be a good idea to also bump to the most recent version of Leaflet when/before doing that.

With kind regards,
Andreas.

[amotl]

When doing this transition, we will have to take care not to lose any changes made to this file on the way [1]. Specifically,
04bcb59 added an autoWidth setting to the Popup options.

// @option autoWidth: Boolean = true
// Set it to `false` if you don't want to compute
// and set the width of a opened popup automatically.
autoWidth: true,

This option, when disabled, will mask the whole section for computing the width for the popup automatically within the _updateLayout method.

if (this.options.autoWidth) {
  style.width = '';
  style.whiteSpace = 'nowrap';

  var width = container.offsetWidth;
  width = Math.min(width, this.options.maxWidth);
  width = Math.max(width, this.options.minWidth);

  style.width = (width + 1) + 'px';
  style.whiteSpace = '';
}

The rationale of this improvement has been outlined at [2] and [3].

Disable automatic width-calculation of popup labels

Toggling the new autoWidthLabels option to false will disable automatic width-calculation of popup labels. This helps controlling the popup rendering not to clip when displayed within narrow-sized maps.

Before/After

---

[1] https://github.com/panodata/grafana-map-panel/commits/develop/src/libs/leaflet.js
[2] https://community.panodata.org/t/grafana-map-panel/121
[3] https://community.hiveeyes.org/t/developing-grafana-worldmap-ng/1824/5

[amotl]

34febf7f extracts the autoWidth feature from the core leaflet.js again. If we are lucky, we can now upgrade to a more recent version of Leaflet. Nevertheless, we should ask upstream to add this feature to its code base.