Major plugin refactor and cleanup.

Switched to POCO library for unified platform/library interface.
Deprecated the external module API. It was creating more problems than solving.
Removed most built-in libraries in favor of system libraries for easier maintenance.
Cleaned and secured code with help from static analyzers.

vendor/CPR/cpr/curl_container.cpp

@@ -0,0 +1,59 @@
+#include "cpr/curl_container.h"
+
+
+namespace cpr {
+template <class T>
+CurlContainer<T>::CurlContainer(const std::initializer_list<T>& containerList)
+        : containerList_(containerList) {}
+
+template <class T>
+void CurlContainer<T>::Add(const std::initializer_list<T>& containerList) {
+    for (const T& element : containerList) {
+        containerList_.push_back(std::move(element));
+    }
+}
+
+template <class T>
+void CurlContainer<T>::Add(const T& element) {
+    containerList_.push_back(std::move(element));
+}
+
+template <>
+const std::string CurlContainer<Parameter>::GetContent(const CurlHolder& holder) const {
+    std::string content{};
+    for (const Parameter& parameter : containerList_) {
+        if (!content.empty()) {
+            content += "&";
+        }
+
+        std::string escapedKey = holder.urlEncode(parameter.key);
+        if (parameter.value.empty()) {
+            content += escapedKey;
+        } else {
+            std::string escapedValue = holder.urlEncode(parameter.value);
+            content += escapedKey + "=";
+            content += escapedValue;
+        }
+    };
+
+    return content;
+}
+
+template <>
+const std::string CurlContainer<Pair>::GetContent(const CurlHolder& holder) const {
+    std::string content{};
+    for (const cpr::Pair& element : containerList_) {
+        if (!content.empty()) {
+            content += "&";
+        }
+        std::string escaped = holder.urlEncode(element.value);
+        content += element.key + "=" + escaped;
+    }
+
+    return content;
+}
+
+template class CurlContainer<Pair>;
+template class CurlContainer<Parameter>;
+
+} // namespace cpr