Thrive - Details page updates

[kkartunov]

-- Generic banner and def image support. When no banner is set use a default image

-- Separated Categories and Tags on the left side column

-- Ads support on the left side of articles

design: https://marvelapp.com/prototype/14fiadgj/screen/81193803

[kkartunov]

@SathyaJayabal fyi

[kkartunov]

QA links:
https://qa-community-app.topcoder-dev.com/thrive/articles/publishing-dart-and-flutter-packages-at-pub-dev-part-1 - no banner image set
https://qa-community-app.topcoder-dev.com/thrive/articles/preparing-to-work-with-datetime-information

[SathyaJayabal]

@kkartunov , the image is cutoff on the bottom

[kkartunov]

@SathyaJayabal this should be fixed. Please re-test...

[SathyaJayabal]

Thanks @kkartunov

[SathyaJayabal]

verified on staging