Needed <script/> tags only

[hcpchris]

In v.1.0.0, Highcharts Maps for Python will generate the full set of <script/> tags that download all of the Highcharts JS modules - whether the visualization uses that module or not.

In v.1.x, it would be good for Highcharts Maps for Python to:

• generate the set of <script/> tags that are strictly necessary for the visualization - if a module is not needed, then it should not be included
• expose a public method for retrieving those <script/> tags for inclusion in a <head/> location
• expose a public method for dynamically retrieving those <script/> tags and appending them to the <head/> location based on Javascript Promises (as is used for the Jupyter Labs rendering in v.1.0.0).

[hcpchris]

This is directly tied to highcharts-for-python/highcharts-core#12.