Spanish translations improvements.

Merged from data sent by Juan Pablo Atienza Martínez
Fix a non consistent text between source and Localizable.strings
Adapt some dimensions in Spanish localizations
Translated ‘Updates:’ in french general preferences
Remove outdated reference to Google in help files (english and french)
French translation : forgotten string on the subscription dialog
Explanations about feed requiring authentification in FAQ help file.

Explanations were added for English and French localizations.
Reorder english and french FAQs from ‘easy’ to technical questions
Updated author’s list
Merge pull request #347 from barijaona/localizations

Translations and help file improvements