Add support for iPhone X

[liuxuan30]

adopted safe area for demo chart controllers;
remove launch image, use launch screen storyboard instead

Note:
I don't apply all constraints to safe area, only for those that will violate the guidelines. For example, slider Y has a decent distance to its super view, so changing to safe area is not a must.

[codecov-io]

Codecov Report

Merging #2967 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2967   +/-   ##
=======================================
  Coverage   19.64%   19.64%           
=======================================
  Files         113      113           
  Lines       13792    13792           
=======================================
  Hits         2709     2709           
  Misses      11083    11083

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[liuxuan30]

CI is fine to merge for old models. I played a little with iPhone X, it's should be fine :)
(the simulator)