Cleanup route segment parsing

[AlexanderNull]

RouteGenerator's parseRouteSegments is a bit unwieldy. We looked into scrapping it in general for 2.0 release however didn't have enough time to work around the somewhat rigid PathMatcher types from Akka-Http. PathMatcher classes are currently tied to objects typed explicitly by the number of matches a path needs to accomplish. As a result we end up having to maintain a lot of match statements which do nothing more than check the length of what's basically a collection of path segments.

Preferred state would be to get rid of the Holder case classes, and simply have a directive that returns a list of the path segment strings. Currently covered this up with paramHoldersToList method but would like to get rid of the more complected code in between.