bump @blueprintjs dependencies

[seve]

This PR bumps all of our BlueprintJS dependencies as follows:

• @blueprintjs/core 3.18.1 -> 3.20.0
• @blueprintjs/icons 3.10.0 -> 3.12.0
• @blueprintjs/select 3.10.0 -> 3.11.2

This fix eliminates console warnings from using renamed/deprecated lifecycle methods.

Note that the following error is still present:

Warning: componentWillMount has been renamed, and is not recommended for use. See https://fb.me/react-async-component-lifecycle-hooks for details.

* Move code with side effects to componentDidMount, and set initial state in the constructor.
* Rename componentWillMount to UNSAFE_componentWillMount to suppress this warning in non-strict mode. In React 17.x, only the UNSAFE_ name will work. To rename all deprecated lifecycles to their new names, you can run `npx react-codemod rename-unsafe-lifecycles` in your project source folder.

Please update the following components: SideEffect(NullComponent)

---

Closes #926