Fixes demo graphs for improved bandwidth estimation

[silltho]

Why is this Pull Request needed?

The demo calculates the bandwidth for each fragment separately from the abr-controller. Therefore it needs to be updated to ensure that the same values are used for the bandwidth estimation and the bandwidth graph on the demo page.

Are there any points in the code the reviewer needs to double check?

Resolves issues:

Checklist

• [x] changes have been done against master branch, and PR does not conflict
• [x] new unit / functional tests have been added (whenever applicable)
• [x] API or design changes are documented in API.md