MIRTH-2722: Fixed bug that prevented code templates from being imported. This is because when the root document is a list, we were still migrating it as if it were a single code template node.

Also, the old ImportConverter has been modified so that it's changing the tag name from "com.mirth.connect.model.CodeTemplate" to "codeTemplate". That isn't necessary because XStream can accept it either way, but it should be done to convert old documents to the correct 2.2.2 XML.

Also also, the alertError call in doImportCodeTemplates has been replaced with alertException so that the user knows why the import failed, instead of just "Invalid code template file."