WIP: first attempt to Improve documentation of the SiSpSeededTrackFinder
This MR resulted from an accidental push to upstream, will open a new one using the fork.
This MR, as part of https://its.cern.ch/jira/browse/ATLIDTRKCP-263, attempts to improve a bit the readability of the track finder top level algorithm.
In particular, comments were added explaining what is being done, and variable names were changed to be hopefully a bit more expressive.
In addition, a few C-style arrays were replaced by std containers in non-performance-critical locations.
This MR should not affect the reconstruction outcome or speed.