[C++][Pistache] Catch exception instead of runtime_error

Created by: muttleyxd

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Description of the PR

Currently method handlers catch std::runtime_error, which directly derives from std::exception. I think it's valid behavior to throw std::invalid_argument from user defined handler, when incoming argument isn't valid. std::invalid_argument is derived from std::logic_error, so it won't get caught by previous catch statement.

Also I fixed catch-value warning, four of these (should I separate this to another PR?)

model/Helpers.cpp: In function ‘bool org::openapitools::server::helpers::fromStringValue(const string&, double&)’:
model/Helpers.cpp:82:21: warning: catching polymorphic type ‘const class std::invalid_argument’ by value [-Wcatch-value=]
   catch (const std::invalid_argument) {

Nothing serious, since exception isn't used anyway