Fix/2929 display date on init

[grzegorz-jazurek]

• fix datepicker don't display initial value in <input> #2929

I found out that Input interceptor for bsValue emit bsValueChange event before bs-datepicker-input.directive is initialised

ngx-bootstrap/src/datepicker/bs-datepicker-input.directive.ts

Line 35 in 4e3e456

this._picker.bsValueChange.subscribe((v: Date) => {

I used setTimeout to move execution at the end of stack.
I'm new in angular 4 so maybe you can use better solution, but main problem is defined above

[codecov]

Codecov Report

Merging #2930 into development will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           development   #2930   +/-   ##
===========================================
  Coverage         70.7%   70.7%           
===========================================
  Files              137     137           
  Lines             4165    4165           
  Branches           737     737           
===========================================
  Hits              2945    2945           
  Misses             914     914           
  Partials           306     306

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[valorkin]

@grzegorz-jazurek thanks a lot for issue and PR!
fixed in a bit different way: #2962