New compiler, new set of warnings...

The main theme here is that clang now checks for range-based for loops
whether it introduces unneeded temporaries, i.e. if the user asks for
a reference for the loop variable, but the iterator doesn't return a
reference or a reference of a different type, or conversely if the
user asked for `const auto`, but could have been `const auto&`.

In practice that usually hits us as:
```
for (const auto& jet : jetContainer)
```
which should be:
```
for (const auto *jet : jetContainer)
```

Also a couple of places like this (which miss the `const` qualifier on
the first template parameter):
```
std::map<std::string,std::string> stringMap;
for (const std::pair<std::string,std::string>& stringPair : stringMap)
```

For the most part I just replaced the loop variable type with what
seemed correct.  In a few places I put explicit comments as to why I
chose the type.

Also a fair number of warnings for unused member variabl...