Gen popup impl. #19

* Added generic pagetemplate, holding "shared" options for popups that
all pagetemplates (can) have
* Created dedicated webmethod for retrieving popup 'sheets' : getsheet,
in favor of getcontent which is also used to retrieve other data such as
rows
* Adding new rows now works again using the add row button
* Webmethod nack now output var_dump instead of json when request is not
a webmethod but "regular" web request.
* Blogentry and Searchresults page now also point to the change layout
popup sheet
* Moved layout sheet popup to generic popup file
* SelectPost optiontype now has possibility to configure enabling
emptyitems, and allows option configurators to set text and value for
the empty item.
* SelectPost optiontype now has feature to show a preview link of the
item currently selected, with options to set the text
* New access checking for webmethods/webservices