Update user.php

Typo corrected:  $this->getHiddenField() was $this->_getHiddenField(
Provide PLG_LIST_ENVELOPE_ENVELOPE string

For dropdown menu in list, this plugin asks for
PLG_LIST_ENVELOPE_ENVELOPE which does not exist.

This commit provides this as the same string as PLG_LIST_EMAIL_EMAIL
which seems to be in error (but which is retained in case it is used by
anyone in eval code).
Added emptyIsh() array helper, considers an array with a single empty
entry as being empty.  Fixes to picklist, to htmlencode JSON'ified
hidden value.  Still working on why picklist isn't retaining value after
failed validation.
Don't show comments for form plugin in PDF view.  Should probably make
this an option, but had a request to hide them in PDF, so for now just
hard wired it.
Merge pull request #985 from Sophist-UK/fix_list_plugin_email_string

Provide PLG_LIST_ENVELOPE_ENVELOPE string
Merge branch 'master' of ssh://github.com/Fabrik/fabrik
Merge pull request #983 from PtrNrs/master

Update user.php
Applying htmlspecialchars() to element labels.
Merge branch 'master' of ssh://github.com/Fabrik/fabrik
fixed: date element edit record with null db date, was incorrectly applying tz offset to null date in getValue();
Merge branch 'master' of github.com:Fabrik/fabrik
Fixing issue with repeat data in calc element.
Merge branch 'master' of ssh://github.com/Fabrik/fabrik
Fixing null rootPath in image element
fixed: contains/not contains for element js events
Merge branch 'master' of github.com:Fabrik/fabrik
adding codestyle
add travis file
fixed: timeline viz: show/hide filters not respected. Click on "today" in calendar didnt alter timeline location
fixed: advanced search, apply, reselect, change element type, - ajax loaded filter value still contained initial selections value