Cleanup code style.

Move ActionReplay code->INI saving into ActionReplay namespace.

Threadsafety Cleanup: ActionReplay is accessed from the Host, Emu
and CPU Threads so the internal storage needs to be protected by a
lock to prevent vectors/strings being deleted/moved while in use by
the CPU Thread.

UI Consistency: Make ARCodes behave like Gecko Codes - only apply
changes when Apply is pressed. Save changes to INI from CheatsWindow.

ISOProperties/CheatsWindow now synchronize with each other.

ISOProperties loads codes using ActionReplay::LoadCodes which actually applies
the codes to the global state. If a game is running then that games receives
all the codes (and ACTIVE status) from the second game being shown in
ISOProperties which is not desirable.

Replaces them with forward declarations of used types, or removes them entirely if they aren't used at all. This also replaces certain Common headers with less inclusive ones (in terms of definitions they pull in).

Various fixes to formatting and whitespace