Feature/content steering optimizations

[dsilhavy]

This PR adds the functionality and changes introduced in version 0.9.7 of the "Content Steering for DASH" specification:

• Adds support for pathway cloning by synthesizing BaseURL and Location elements
• Adds support for steering Location and PatchLocation. A new LocationSelector was introduced for this purpose.
• DASH_throughput and DASH_pathway now include a comma separated list of the throughput values for all serviceLocations used between two steering requests.
• Adds support for multiple Location and PatchLocation elements. Previously, dash.js was only using the first element and ignored all others.
• Add support for ContentSteering defined in ServiceDescription elements.
• Query parameters defined as part of the PATHWAY-CLONES are appended to the respective requests.
• Server side errors 410 and 429 are handled according to the specification
• Attributes have been renamed according to version 0.9.7 of the specification
• Multiple model classes were introduced for ContentSteering, ContentSteeringResponse, PatchLocation, MpdLocation.
• The content steering sample page was adjusted to visualize the selected CDNs dynamically based on the available options.