Removed old / unnecessary code

* Removed Plugins.h file as I assume setting up a plugin hell is a bad
idea (does anyone disagree?).
* Removed FnIdGenerator, and moved FnIdGenerator::GenerateFnId to
getFunctionId in Modules.cpp
* Disabled RSX Debugger and Memory Viewer when the emulator is stopped.
* ELF64Loader::LoadPhdrData refactored.