Restructure per-core configs.

Merging yesterday was probably a bit premature.

One issue I overlooked was that per-core configs were not flushed to disk
when loading a new core on PC. The per-core flushing only happened on
main_exit(), which is only run on application termination. This hence
would only work with consoles with exitspawn.

config_set_defaults() must be called when loading per-core-specifics as
well or lots of options silently leak into other core specific configs
when cores are changed.

The handling with g_extern.config_path and original_config_path was
difficult logic and very error prone considering it was mutated aribitrarily by RGUI.
I've removed the original config path concept and stuck
with that config_path is *only* for global config, and
core_specific_config_path is for core-specifics (which are resolved
during config load). Saves some memory too,
which is always nice.

The block_config_read solution I proposed yesterday was not good after
all (in fact, broken on PC), and the current solution should work better.

"RetroArch Config" option in RGUI now only shows global config.
Only save per-core configs when core specific option is enabled.

Also, need to enforce that g_settings.core_specific_config is true
after loading core specific config. It's possible that core specific
option is set to false before loading a different core (using global
config only).
Merge pull request #459 from libretro/per-core-config2

Restructure per-core configs
Merge pull request #460 from lioncash/master

Indicate downloadable cores are still in development for the Android front-end.
No longer going to maintain separate READMEs for console ports
(Android) Bump up version code to 26 - bump up version number to 1.0.0.0
(iOS) Make cocoa menu button image show up more constantly.
Add support for mapping keyboard keys to input overlays.
Update build zips for win.
(Android) Links to documentation changed
(Overlay Keyboard) Use 1 bit per key to store state.
Only call rarch_main_deinit if main has been initied.
Fix unpack row len with 16-bit cores on desktop.

Missed call to UNPACK_ROW_LENGTH :(
Use core-specific config path for RGUI cgp/glslp if applicable.

Avoids some collisions.
replace retroarch.png with updated logo and added icns version
wipe out bad changes
add osx/ios icns
Merge pull request #464 from hizzlekizzle/master

better commit for ios/osx icns
(OSX) Update OSX port to use new icon
(iOS) Replace icons