Circular dependencies warnings during build

[bhufmann]

When building the application from the root directory with yarn, the following me warning messages are shown and should be addressed:

browser-theia-trace-example-app: WARNING in Circular dependency detected:
browser-theia-trace-example-app: ../../theia-extensions/viewer-prototype/lib/browser/trace-explorer/trace-explorer-contribution.js -> ../../theia-extensions/viewer-prototype/lib/browser/trace-explorer/trace-explorer-widget.js -> ../../theia-extensions/viewer-prototype/lib/browser/trace-explorer/trace-explorer-sub-widgets/theia-trace-explorer-opened-traces-widget.js -> ../../theia-extensions/viewer-prototype/lib/browser/trace-viewer/trace-viewer.js -> ../../theia-extensions/viewer-prototype/lib/browser/trace-explorer/trace-explorer-contribution.js
browser-theia-trace-example-app: WARNING in Circular dependency detected:
browser-theia-trace-example-app: ../../theia-extensions/viewer-prototype/lib/browser/trace-explorer/trace-explorer-sub-widgets/theia-trace-explorer-opened-traces-widget.js -> ../../theia-extensions/viewer-prototype/lib/browser/trace-viewer/trace-viewer.js -> ../../theia-extensions/viewer-prototype/lib/browser/trace-explorer/trace-explorer-contribution.js -> ../../theia-extensions/viewer-prototype/lib/browser/trace-explorer/trace-explorer-widget.js -> ../../theia-extensions/viewer-prototype/lib/browser/trace-explorer/trace-explorer-sub-widgets/theia-trace-explorer-opened-traces-widget.js
browser-theia-trace-example-app: WARNING in Circular dependency detected:
browser-theia-trace-example-app: ../../theia-extensions/viewer-prototype/lib/browser/trace-explorer/trace-explorer-widget.js -> ../../theia-extensions/viewer-prototype/lib/browser/trace-explorer/trace-explorer-sub-widgets/theia-trace-explorer-opened-traces-widget.js -> ../../theia-extensions/viewer-prototype/lib/browser/trace-viewer/trace-viewer.js -> ../../theia-extensions/viewer-prototype/lib/browser/trace-explorer/trace-explorer-contribution.js -> ../../theia-extensions/viewer-prototype/lib/browser/trace-explorer/trace-explorer-widget.js
browser-theia-trace-example-app: WARNING in Circular dependency detected:
browser-theia-trace-example-app: ../../theia-extensions/viewer-prototype/lib/browser/trace-viewer/trace-viewer.js -> ../../theia-extensions/viewer-prototype/lib/browser/trace-explorer/trace-explorer-contribution.js -> ../../theia-extensions/viewer-prototype/lib/browser/trace-explorer/trace-explorer-widget.js -> ../../theia-extensions/viewer-prototype/lib/browser/trace-explorer/trace-explorer-sub-widgets/theia-trace-explorer-opened-traces-widget.js -> ../../theia-extensions/viewer-prototype/lib/browser/trace-viewer/trace-viewer.js