Reduce complexity of simplify filter (#1149)

Reduce complexity of simplify filter (#1149)

* fix bugs with simplify filter

1. With the length option the last point deleted took the total error
over the specified limit.

2. When computing the total error if another point is deleted it was
possible to refer to an xte record that needed to be updated due to
the deletion of one of its neighbors.

* wip on reduced complexity simplify filter.

* mimic ineheitence of new_trkseg flag in simplify filter.

* cleanup simplify header.

* work around apparent Qt5 QMap bug.

* fix shadowing issues.

* astyle

* correct spelling.

* kill Waypoint route_priority.