Date form elements are now stored as BIGINT, fixes sorting bug

All language files updated

manage_fields.php
using new PDb_FormElement::get_datatype() method

participants-database.php
latest Db version is now 0.8
set_form_element() has been moved to xnau_FormElement class and is called from PDb_FormElement as PDb_FormElement::get_datatype($form_element)

PDb_FormElement class
print_hidden_fields() now returns the whole series of hidden fields as a single string

PDb_Init class
using new PDb_FormElement::get_datatype() method
DB update: all date fields are now stored as BIGINT

PDb_Shortcode class
retooled _empty() method...it was buggy, now it returns true only if the value is NULL or empty string. It was returning empty for 0, now it won't.

xnau_FormElement class
added get_datatype() method: moved here from the main script

git-svn-id: https://plugins.svn.wordpress.org/participants-database/trunk@815583 b8457f37-d9ea-0310-8a92-e5e31aec5664