backport: Use range-based for loops (C++11) when looping over map ele…

[fdoving]

…ments

manual backport of bitcoin #10493
picked: 680bc2cbb34d6bedd0e64b17d0555216572be4c8

Origial-author: practicalswift

Before this commit:

for (std::map<T1, T2>::iterator x = y.begin(); x != y.end(); ++x) {
}

After this commit:

for (auto& x : y) {
}

[hans-schmidt]

These changes are functionally identical to what bitcoin did. (There are two extra changes in wallet.cpp related to IsAssetScript, and some bracket reformatting).
This doesn't actually do anything except update some code to cleaner C++11 syntax.
Approved.

[HyperPeek]

approved, cleanup using c++11 features in loops with no functional change