Some fixes as suggested by clang-tidy.

- Cleaned up std::move usage

This includes removing invocations where it does not have any impact,
e.g., moving ints or arrays. I also added std::move calls for types
where it improves performance, such as strings or std::vector.

- Added noexcept modifier to move constructors

- Added parentheses where they were missing.

- Added pointer qualifier to auto declarations

- Added checks to prevent broken objects in case of self
  assignments

For example for TaintFlow the assignment constructor first releases
its own resources. If a self assignment TaintFlow f = flow; takes
place, this would mean we release the resources and then try to use
them, which is obviously problematic.

- Removed some superfluous copies by using references.