fix to enable import of answers from a different installation/version of LS
Corrected a typo on variable name (table_start_index).
Made fallback import optionnal and disabled by default.
Added code to check if at least one answer field could be imported
before committing import.
Make sure the number of columns is sufficient in force import.
A few styling changes.
Merge pull request #138 from Grapsus/fix_import

enable LS to import answers (.vv) between different installations/versions