Remove support of:
- Theme Amelia: removed with bootstrap 3.3.0, but released in odoo at
bootstrap version 3.2.0 (should have been removed since Odoo 9.0
(boostrap version 3.3.5))
- Theme Readable: removed with bootstrap 4.0.0 so it is best to remove
it now so as we are gonna migrate to bootstrap 4.0.0.
We may want to add new bootswatch theme with bootstrap 4.0.0 migration.
This commit also adds the missing LICENSE file.