Issue description

(This is a followup to issue#241 which was partially resolved by#246)

Now that there is a chunk context menu (as of#246) with support for basic operations such as showing/hiding selected chunks, there's a good foundation for adding the ability to implement the ability to filter to filter to related chunks (e.g. parents/siblings).

This task involves:

• Clearly defining and documenting relationships between chunks: what a Webpack "parent" or "sibling" chunk is (andhow the chunk graph differs between Webpack 3 and 4)
• Adding new context menu options to filter to parents and siblings
  • This changeset shows where I reverted changes that add a "filter to parent" option:c9bae5b. Adding back that particular option might just mean re-applying those changes and then documenting clearly.
• Testing the new options on multiple Webpack project setups (e.g. with various configurations of common chunks/split chunks, dynamic imports)
• Considering how else the UI could be changed to make the new options clear. e.g. when a context menu option is hovered, highlight all of the currently-visible chunks that would be filtered to?