Improve filelist summary

 - Remove bottom border of summary

 - Increase padding of summary

 - Use text instead of '&'

 - No hover effect for the filelist-summary

 - Improve l10n aspects

 - Apply padding to top and bottom

 - Use background-color: transparent;

Fix #993
Reimplement filesummary in JS
Add plural translations
Several improvements

 - Remove summary if it's "empty"

 - Properly check if count is 0

 - Reshow html if it was hidden before

 - Remove simpleFileSize() | See #4118

 - Use n() instead of tp()