Optional disable of pop action on setting route

[lukefanning]

I started playing around with this router for a WatchKit app I'm going to be working on. I realised that the router could not handle back button / swipe left navigation patterns without also triggering the pop func on the Routable when dispatching a SetRouteAction on willDisappear() (similarly to the GitHubBrowserExample). This PR takes an alternative approach to solving it by specifying a disablePopAction bool on the SetRouteAction. This means the pop() isn't called but the routable is removed from the array. Seems to work well from testing on a real Apple Watch.

[codecov-io]

Codecov Report

Merging #126 (03272ae) into master (5231c3e) will decrease coverage by 3.13%. The diff coverage is 26.31%.

@@            Coverage Diff             @@
##           master     #126      +/-   ##
==========================================
- Coverage   92.74%   89.60%   -3.14%     
==========================================
  Files           8        8              
  Lines         634      481     -153     
==========================================
- Hits          588      431     -157     
- Misses         46       50       +4     

Impacted Files	Coverage Δ
ReSwiftRouter/NavigationState.swift	100.00% <ø> (ø)
ReSwiftRouter/Router.swift	79.52% <10.00%> (-5.25%)	:arrow_down:
ReSwiftRouter/NavigationReducer.swift	81.48% <28.57%> (-18.52%)	:arrow_down:
ReSwiftRouter/NavigationActions.swift	100.00% <100.00%> (ø)
...iftRouterTests/ReSwiftRouterIntegrationTests.swift	89.68% <0.00%> (-0.98%)	:arrow_down:
ReSwiftRouterTests/RouteHashSpec.swift	100.00% <0.00%> (ø)
...SwiftRouterTests/ReSwiftRouterTestsUnitTests.swift	100.00% <0.00%> (ø)

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