Vis Svelte | Fix component lifecycle logic

[reb-dev]

Fixes #86

@rokotyan I spent some time investigating this and it seemed like the best thing to do was to change the way we handle component lifecycles in our svelte wrapper.

Before:

• onMount: the setter method provided by the container is called (i.e. setAxis) which updates the container's config.
• onDestroy: the same method is called with undefined to remove it from the container's config. This created a unique issue for axis because we need to know which config key (i.e. xAxis or yAxis) to make undefined. A workaround could have been to make an additional method called removeAxis but that seemed convoluted to me. I wanted to rethink our current approach and further separate the component logic from the container's.

Changes:

• The component mounts/destroys independent of the container, but uses the action provided by the container as a side effect. So now after the axis mounts, the container will determine its type and create the onDestroy that will be called later.
• The destroy() method is called on the wrapped components themselves now. I'm not sure how important it is but I realized we didn't do that before like we do in our react wrapper.