Merge pull request #413 from alexsalas/master

Added spanish as new lenguage
Various bugfixes and improvements.
Cleanup readers.xml in Spanish.
Fix #395 - next/previous buttons in translations.
Swap previous and next buttons in translations.
Bump vesion to 2.5.7, update strings.
Merge pull request #1 from quran/master

Vesion to 2.5.7