Mqtt 5

[mman]

Closes #450 to support integration of https://github.com/victronenergy/victron-mfd-modules/pull/18

After much investigation it turns out that two fixes are required:

1. Importing polyfill for AbortSignal and AbortController. That one is pretty straightforward.
2. Transforming XXXn JS bigint literals to BigInt("XXX") to avoid syntax errors in older browser.
3. Importing polyfill for globalThis from @ungap/global-this. That one is not straightforward at all because we are already compiling the app with webpack/babel/babel-loader and targeting Chrome >=45, so resulting JavaScript correctly includes globalThis polyfill from core-js library. It is also used where needed. But turns out that babel in our build is getting confused somehow and does not properly reference the globalThis polyfill in mqtt dependency.