Removed external functions from SysCalls.h

* Replace `int` with `s32` as return type for syscalls.
* 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.
* Splitted some 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 external functions from `SysCalls.h`.

NOTE: What should we do about: cellGcmCallback? It's not a lv2 syscall
but it appears on the sc_table and it is actually called in games. Is
this some kind of hack?
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.
Fixed conflicts and minor changes (2)
Merge pull request #396 from DHrpcs3/prx_loader

Changes for modules and lv2 sycalls