[C++][Pistache] Fix optional error and wrong function signatures (#264)

* Added missing includes for optional

* Removed shared pointer from pistache generator

* Changed Net namespace to Pistache Namespace

* Clean up code and removed unnecessary lines in mustache files

* Removed remaining shared pointer syntax

* Code review fixes + updated samples

* Added const to all model setter functions, and reference to all params in setters that are not primitives

* Refactored modelbase

* Removed const

* Updated samples

samples/server/petstore/cpp-pistache/model/ModelBase.cpp

@@ -23,41 +23,41 @@ ModelBase::~ModelBase()
 {
 }
 
-std::string ModelBase::toJson( const std::string& value )
+std::string ModelBase::toJson( std::string const& value )
 {
     return value;
 }
 
-std::string ModelBase::toJson( const std::time_t& value )
+std::string ModelBase::toJson( std::time_t const& value )
 {
     char buf[sizeof "2011-10-08T07:07:09Z"];
     strftime(buf, sizeof buf, "%FT%TZ", gmtime(&value));
     return buf;
 }
 
-int32_t ModelBase::toJson( int32_t value )
+int32_t ModelBase::toJson( int32_t const value )
 {
     return value;
 }
 
-int64_t ModelBase::toJson( int64_t value )
+int64_t ModelBase::toJson( int64_t const value )
 {
     return value;
 }
 
-double ModelBase::toJson( double value )
+double ModelBase::toJson( double const value )
 {
     return value;
 }
 
-bool ModelBase::toJson( bool value )
+bool ModelBase::toJson( bool const value )
 {
     return value;
 }
 
-nlohmann::json ModelBase::toJson( std::shared_ptr<ModelBase> content )
+nlohmann::json ModelBase::toJson(ModelBase content )
 {
-    return content.get() ? content->toJson() : nlohmann::json();
+    return content.toJson();
 }
 
 }