Changes for modules and lv2 sycalls

I know the branch is called PRX Loader, but I would like to push some *snacks* before the bigger changes come.

Controversial changes may be:
* Replace `int` with `s32` as return type for lv2 syscalls. Basically because `sizeof(int)` is not fixed, but `sizeof(s32)` is. (Or I am just too paranoid about what the future holds?)
* Renamed `SC_Something.*` files with the proper lv2 name `sys_something.*`.
* Moving away from the lv2, those functions and folders that doesn't correspond to lv2 functions. E.g. module functions from *sys_io*, *sysPrxForUser*, *cellGcmSys* where in lv2/ even if they aren't lv2 syscalls.
* Splitted some lv2 files (*memory* -> *memory*+*mmapper*) and merged other ones (*event*+*event_flag* -> *event*, *spu*+*spu_thread* -> *spu*), according to common sense, PSDevWiki docs, and checking firmware files.
* Removed *extern* functions from `SysCalls.h`. Instead, we include lv2 syscall source headers with the function declarations.
* Removed *Plugins.h* file as I assume setting up a plugin hell is a bad idea. (CC. @DHrpcs3).
* Removed FnIdGenerator, and moved FnIdGenerator::GenerateFnId to getFunctionId in Modules.cpp (CC. @O1L)

Harmless changes are:
* Disabled *RSX Debugger* and *Memory Viewer* when the emulator is stopped.
* ELF64Loader::LoadPhdrData refactored.

I do the pull request just for checking if anyone disagrees with any of the changes made (including TravisCI :wink:), but that doesn't mean it's ready to be merged now.