Added spreadsheet directory & spreasheet creation
Added catalog_id to Course
Course Controller is now creating course object with catalog_id
Replaced excell gem by spreadsheet one
Catalog is now printing course informations into xls file
Catalog is now handling correctly xls data headers
Added catalog upload controller action and coresponding (post) route
Aded spreadsheet filename field to catalog model.
Modified Catalog seed filename format
Fixed bug in catalog upload form
Catalog is now deleting old spreadsheet when uploading new one
Xls parser allow now user to update course information
Parser converts now cells element to string before adding it into the database
The .xls uploaded is now adding information from modules and sub modules
Removed useless methods in Catalog Model
PModules and SubModules properties can now be updated through xls parser
Updated todo file
Fixed parameter bug in PModule Controller
Refactored PModule show view
Fixed parameter bug in SubModule Controller