W3C compliance (work on issue #64 - https://github.com/shaarli/Shaarli/issues/64):

  * fix duplicate IDs - #paging_older, #paging_newer become classes as the paging is displayed twice (top, bottom) in the linklist
  * fix duplicate IDs - #paging_privatelinks and #paging_linksperpage become classes
  * daily links are now valid (use &amp)
  * name attribute is not used anymore on a tag in link list
  * center tag is replaced by CSS in picwall and tag cloud
  * action in form tag can't be empty, use # instead
  * fixed configure table with CSS instead of cellpadding, border, and valign
  * export links are now valid
  * remove "size" in input tag
  * Fix missing alt attributes for img elements
  * tpl/daily: Use HTML entities instead of char escape codes
  * tpl/export: fix missing </span> closing tag
  * Remove obsolete language attribute on <script> elements