New option onread_jump_next

Added a new option to automatically jump to the next sibling (category
or feed) when hitting the button "mark as read".
Typo
Merge branch 'onread_jump_next' of https://github.com/Alkarex/FreshRSS into Alkarex-onread_jump_next
Issue #143 : amélioration du formulaire

Suppression radio buttons au profit d'une checkbox