[IMP] website.snippet: create automatically the thumbnail; data-option became data-js; add data-eval method; rename check_class into toggle_class
[FIX] website.snippet: the background option is not readily usable by the designer
Merge pull request #2050 from odoo-dev/master-theme-review-chm

[IMP] website.snippet: create automatically the thumbnail; fix background
 This is a combination of 2 commits.

[ADD] account, account_bank_statement_import: Adding onboarding tips futures (account_tip_data.xml, account_import_tip_data.xml files).