Allow Specifiying an Event for Anchor field

[aanunez]

Some end-users are using the EM by recording 1 month of data per event. Right now they have to use a field system like cal_data_1, cal_data_2 etc because associating all of the calendar with a generic "cal_data" will overwrite the config as we pull it in from PHP. To resolve this we should have an optional Event var along with the anchor field.