This PR modernizes the code in Poco::Util by using more C++ 11 and later idioms such as

• type aliases
• deleted and defaulted special member functions
• override annotations
• auto variables
• range-for loops
• default member initializers
• constructor delegation
• initializer lists
• lambdas

It also does some refactoring to reduce duplicated code:

• In classes Application and ServerApplication, arguments of form int argc, char** argv or int argc, wchar_t** argv are now immediately transformed into a canonical ArgVec before doing anything substantial. No longer
  is there duplicated code in (for example) int ServerApplication::run(int argc, char** argv),
  int ServerApplication::run(const ArgVec& args), and int ServerApplication::run(int argc, wchar_t** argv).

• Since ConfigurationView and LocalConfigurationView have almost identical code, they now derive from an intermediate class AbstractConfigurationView that provides the common methods.

SystemConfiguration now uses an explicit map of functions instead of long if-else chains. Since all tags
are used only once, we no longer need to define them in a list of static const std::string variables.

AbstractConfiguration::keys, Application::getApplicationPath and Application::getApplicationDirectory
got overloads that return the requested information instead of filling a provided data structure. The old
versions still exist for downward compatibility. (I assume they exist because it was expensive before C++11 to return a large data structure from a function.)

Overall the PR reduces the code size by about 500 lines and makes it more maintainable and easier to read.