Various l10n fixes for /firefox/new
* remove an unused span tag in title while we already have the string without this tag localized
* add typographic quotes in a sentence because we have that string with those quotes
* split a string into 2 strings we already have
* make alt text and page title translatable
* remove white space in string to facilitate conversion of existing strings
Merge pull request #767 from pascalchevrel/firefox_new_various_l10n_fixes

Various l10n fixes for /firefox/new