Add missing STL includes and remove redundant and unused ones

[JaxonWasTaken]

This should prevent any issues like #42 occurring again due to changes in STL implementations or refactors of RMG.

Summary of changes

Soruce/RMG-Audio/main.cpp:

• <cstdlib> for malloc(), free()
• <cstdint> for uint8_t

Source/RMG-Core/Core.cpp:

• <string> for std::string

Source/RMG-Core/Directories.cpp:

• <cstdlib> for std::getenv()

Source/RMG-Core/Key.cpp:

• <string> for std::string

Source/RMG-Core/MediaLoader.cpp:

• <cstdint> for uint8_t

Source/RMG-Core/Plugins.cpp:

• redundant <string> as it is included in the associated header

Source/RMG-Core/Rom.cpp:

• <cstdlib> for malloc(), free()
• remove unused <iostream>

Source/RMG-Core/RomHeader.hpp:

• change <cinttypes> to <cstdint> because extras aren't used

Source/RMG-Core/RomSettings.hpp:

• change <cinttypes> to <cstdint> because extras aren't used

Source/RMG-Core/Screenshot.cpp:

• <string> for std::string

Source/RMG-Core/Settings/Settings.cpp:

• remove unused <exception>
• remove redundant <string> as it is included in the associated header

Source/RMG-Core/SpeedLimiter.cpp:

• <string> for std::string

Source/RMG-Core/VidExt.cpp:

• <string> for std::string

Source/RMG-Core/Video.cpp:

• <string> for std::string

Source/RMG/Callbacks.hpp:

• <string> for std::string

Source/RMG/UserInterface/Dialog/SettingsDialog.hpp:

• <string> for std::string
• <vector> for std::vector

Source/RMG/UserInterface/Widget/OGLWidget.cpp:

• remove unused <iostream>

Source/RMG/UserInterface/Widget/RomBrowserWidget.cpp:

• <vector> for std::vector

[Rosalie241]

Thank you :heart: