big work on templates

== ABOUT TEMPLATES ==
-> unified the format of user and master templates
-> 'externalname' has been changed to 'template'
-> user templates have static labels while master templates uses multilang labels
-> editing teachers (or teacher, I do not remember, it is matter of permissions) can create user templates as far as master templates.
-> the restore method for user and master templates both, is the same
-> the creation method for user templates is a subset of the process to create a master tempalte
-> the list of labels is defined per each item in the method: item_get_multilang_fields
-> The '_sid' fields were not deleted because they are crucial to get the multilang content
-> The suggested 'multilang' fields is, hence, no longer needed and has not been added
-> the "restore multilang content" has been added at item level in the item management page (only for item where multilang is applicable)
-> the installation of master templates is still requested even if no more items are added to the database at installation time
-> almost 300 rows of code were deleted thanks to this great idea from my great supervisor. Thank you. (I know you are reading this comment). :-)
The idea is this:
:: apply a master template
:: fields having corresponding '_sid' are leaved EMPTY.
:: the content of each field having corresponding "_sid" is gathered at item load time from lang files
:: user is allowed to change the multilang contents to a static content by editing and saving them in the usual way
:: '_sid' and 'template' are never touched. They are the source of information to find the content of multilang fields

== OTHER MINOR ISSUES ==
-> uniformed classes names: i.e.: 'surveyitem_base' has been renamed to 'mod_survey_itembase'
-> item_delete_item: the param $displaymessae in itembase.class.php was never used. It has been removed.
-> renewed the way to get item in itemlist.class.php
-> renewed the way to get item content in manage_item_* in itemlist.class.php
-> introduced the parent class mod_survey_templatebase. It is the parent of mod_survey_usertemplate and mod_survey_mastertemplate
-> changed the name of the class inside master templates folder from survey.class.php to template.class.php (it is still never used)
-> dropped the incredible, useless, wrong defaultvalue_sid for numeric items
-> changed the ugly 'fslabel' fieldset field name to the simpler 'label'
-> changed the ugly 'fslabel_sid' fieldset field name to the simpler 'label_sid'