fix(datepicker): update activeDate on select

[fmalcher]

I wanted to use angular reactive forms and update the form value from within the component.
However, the date picker does not update its view then. This PR fixes the problem.

I saw there's a new datepicker as work in progress – great! 🎉
Would be nice if you could merge this small fix for the meantime!

Best, Ferdinand

[codecov-io]

Codecov Report

Merging #1676 into development will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff              @@
##           development    #1676   +/-   ##
============================================
  Coverage        84.84%   84.84%           
============================================
  Files               85       85           
  Lines             2323     2323           
  Branches           299      299           
============================================
  Hits              1971     1971           
  Misses             252      252           
  Partials           100      100

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[valorkin]

Thanks ;)