Clean READMEs

[igor-dv]

Issue: There is a few copy-pasted content from place to place, that is being hard to maintain because there is no single source of truth

What I did

1. Removed badges from the inner packages (there was even broken greenkeeper badge somewhere)
2. Commented out the BrowserStack since it is not implemented.
3. Removed unused ancient images
4. Moved all the copy-pasted demo.gifs to one place. If any framework want its own (like in marko), then it might be changed. I would even prefer some abstract Storybook drawings, because UI changes frequently

[codecov]

Codecov Report

Merging #3939 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3939   +/-   ##
=======================================
  Coverage   39.64%   39.64%           
=======================================
  Files         431      431           
  Lines        5449     5449           
  Branches      740      740           
=======================================
  Hits         2160     2160           
  Misses       2906     2906           
  Partials      383      383

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[ndelangen]

Nice cleanup!