New import handler (ContactEmailHandler) and other fixes

* Seeing as some imports require providing the email of a contact,a new subclass of columnhandler has been made to handleand validate just this.* Messing up the type header (blank, wrong, or completely missing)will not give better warning* When user tries to import a blank csv file, a blank previewtable will be shown but an appropriate error will be shown above* Style changes and minor refactors that jumped out at mewhere I was working