Add the ability to import scenarios from older versions of PerfCake

[pmacik]

There is a XSLT template that can be used to convert scenarios from version to next version (as of October 2014 the template is only from version 2 to version 3).

When opening a scenario that is from older version of schema now the error is thrown and the editor
does not open it. The user should get error message that the scenario that he is opening is from older version and get the option to either close it or let the plugin to convert it to the current version (using the XSLT that is part of perfcake jar).