fix bug cloning choice_fields

this affected choice_fields with conditional elements

I was using the conditional_id column for the new implementation of
conditional elemnts, thinking conditional_id wasn't used.  Turns out
some choice fields were still using conditional_id and rather than
using the one column for two purposes, I made a new choice_field_id
column.  This will ensure apps that use the previous method of doing
conditional elements still work.

Apps using fe will have to use run fe_engine:install:migrations to
install the migration
Merge branch 'fe' of github.com:CruGlobal/qe into fe