[Bug] The shimmer loading indicator doesn't match with the design

[minhnimble]

Why

The application needs to show the initial skeleton loading view with animation after first entering the app with a valid logged in session like design. Currently there are a few problems with the initial skeleton loading screen:

• The color and corner radius of the skeleton items doesn't match with the design and there is no gradient feeling.
• The next button in the bottom right corner is not shown correctly in circle shape.
• Missing many animation frames on the top and bottom part of the skeleton loader.

Acceptance Criteria

• The skeleton loading view needs to look like the following design while it is being shown:

https://github.com/hsu-hsu/nimble-survey-app/assets/70877098/fa55f83e-ad63-4da2-8a3f-60148209f8d1

Actual:

https://github.com/hanluong/NimbleiOSChallenge/assets/70877098/11247fdd-aa0e-4858-a000-d51dba14566d

[hsu-hsu]

I change shimmer view color and add necessary view and remove extra view as design. pull request -> #26