Update es_ES.ini

Translated credits and plugin download section. Added missing strings from savestate warnings. Other minor fixes.
Update es_ES.ini

Added "Buy PPSSPP Gold" translation.
Update es_ES.ini

Edited some lines to fit button width. Remove some uppercases. Edit meaning in a couple of strings.
Merge pull request #81 from ppmeis/patch-10

Update es_ES.ini