[ticket/12342] Use prop() instead of attr() for boolean properties

PHPBB3-12342
[ticket/12342] Fix Find a member show / hide script

PHPBB3-12342
[ticket/12342] Fix the Custom Dates function in UCP Prefs Global

Function was being called before dE() function exists,
causing it to fail. Should be called when the page/window
is ready.

PHPBB3-12342
[ticket/12342] Remove spinner and fix useage of ajax on memberlist

PHPBB3-12342
Merge remote-tracking branch 'vsephpbb/ticket/12342' into develop-ascraeus

* vsephpbb/ticket/12342:
  [ticket/12342] Remove spinner and fix useage of ajax on memberlist
  [ticket/12342] Fix the Custom Dates function in UCP Prefs Global
  [ticket/12342] Fix Find a member show / hide script
  [ticket/12342] Use prop() instead of attr() for boolean properties