Added XLSX support, optional row validation, added SQLite insert_update_db

1. Added xslx support through Roo gem.
  * [Roo](https://github.com/Empact/roo) appears to be more fully featured than [Spreadsheet](https://github.com/zdavatz/spreadsheet), and it supports XLSX files whereas the latter does not.  Other than that it seems to be a drop-in replacement.
2. Made row validation optional on ExcelParser.
  * I was running into issues where it's no big deal for my script to be smart enough to skip invalid rows but the whole ETL job would barf because one row was missing a field.  putting `:validate => false` in the parser options will skip row-level validation.
3. Added SQLite3 to the `insert_update_database` destination.  It works.
4. The changes to `engine.rb` are for ActiveRecord 3.2.x, which will not allow mass-assignment unless expressly enabled on the model.  This change seemed easier than modifying the model class `ETL::Execution::Job` since I didn't know what might break if I change that class around.