Cleans up the JIT block viewer in the WX UI.

This code was an absolute mess. It had allocated an arbitrarily large string buffer to hold instructions that were disassembled.

Strip out all of the nasty raw C string manipulation and replaces it with ostringstream usage.
Fixes an issue where if you didn't have a JIT recompiler running then Dolphin would instantly crash if you tried comparing PPC to x86 code.
Changed the disassembly of the host side code from being inline to the function to instead being in a class, this will be required when I add support
for ARMv7 and AArch64 to this window.
Indentation of public and private is a little off here (as well as in HostDisassembler above)