Removed several mutable members by templatising the non type specific code
Added "const" specifier to all methods. Required removing a member (simtrackid) that is only ever used a local variable.
Got rid of the last mutable members and overhauled large chunks of the type handling
Revert some whitespace changes
Merge pull request #3639 from mark-grimes/makeQuickTrackAssociatorThreadSafe

Sim -- Make QuickTrackAssociatorByHits thread safe