add insertCard and appendCards methods

[mac-gallagher]

• Add the following methods the SwipeCardStack:
  • func numberOfRemainingCards() -> Int
  • func insertCard(atIndex index: Int, position: Int)
  • func appendCards(atIndices indices: [Int])
• Rename position(forCardAtIndex index: Int) method to positionforCard(at index: Int)

This addresses #13

[codecov-commenter]

Codecov Report

Merging #89 into master will increase coverage by 0.6%.
The diff coverage is 100.0%.

@@           Coverage Diff            @@
##           master     #89     +/-   ##
========================================
+ Coverage    82.5%   83.1%   +0.6%     
========================================
  Files          13      13             
  Lines         663     687     +24     
========================================
+ Hits          547     571     +24     
  Misses        116     116             

Impacted Files	Coverage Δ
...Shuffle/SwipeCardStack/CardStackStateManager.swift	100.0% <100.0%> (ø)
...ources/Shuffle/SwipeCardStack/SwipeCardStack.swift	99.4% <100.0%> (+<0.1%)	⬆️