updated libs
switch back to pickle serializer for compatibility
partial implementation of export to excel
export to excel from command line
Revert "partial implementation of export to excel"

This reverts commit 3accf045dfc31105ea91377d1aaa981b3f521521.
Merge branch 'specs': export to excel from command line
rename dev database
Merge remote-tracking branch 'origin/stable'
Merge branch 'django16'
Merge remote-tracking branch 'origin/stable'
load categories in db and update specs
drop all product specifications
add category with specs file upload in admin
read specs excel and update database
show specs in product web page
product specifications design
move specs function in model
do not show None spec group
import all sheets
preserve specs order as in excel