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/POCO/CONTRIBUTORS

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+Guenter Obiltschnig
+Alex Fabijanic
+Peter Schojer
+Ferdinand Beyer
+Krzysztof Burghardt
+Claus Dabringer
+Caleb Epstein
+Eran Hammer-Lahav
+Chris Johnson
+Sergey Kholodilov
+Ryan Kraay
+Larry Lewis
+Andrew J. P. Maclean
+Andrew Marlow
+Paschal Mushubi
+Jiang Shan
+David Shawley
+Sergey Skorokhodov
+Tom Tan
+Sergey N. Yatskevich
+Marc Chevrier
+Philippe Cuvillier
+Marian Krivos
+Franky Braem
+Philip Prindeville
+Anton Yabchinskiy
+Rangel Reale
+Fabrizio Duhem
+Patrick White
+Mike Naquin
+Roger Meier
+Mathaus Mendel
+Arturo Castro
+Adrian Imboden
+Matej Knopp
+Patrice Tarabbia
+Lucas Clemente
+Karl Reid
+Pascal Bach
+Cristian Thiago Moecke
+Sergei Nikulov
+Aaron Kaluszka
+Iyed Bennour
+Scott Davis
+Kristin Cowalcijk
+Yuval Kashtan
+Christopher Baker
+Scott Davis
+Jeff Adams
+Martin Osborne
+Björn Schramke
+Francis Andre
+Kacper Piwiński