Since 12.0, the theme was still supported but did not receive any of the
new features, like choosing its own colors.

This commit removes the theme entirely so that all users use the new
shiny features and also because it will become impossible to support
with the new color system.

task-2207192

closes odoo/odoo#51508

Related: odoo/design-themes#279
Related: odoo/upgrade#1225
Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>

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.

This is a simple renaming without adaptation.

Reorganize the theme folder to follow standard hierarchy. In particular,
the libs are now placed in a dedicated folder in the /static/lib folder
instead of the /static/src folder.

website.snippet: The methods described in javascript will be called automatically from the data-method_name = value on li snippets options. The methods are called in the order relative to children of xml (eg: <li data-method1=value1> ... <li data-method2=value2> ... </ li>, the method1 is then called method2). Methods receive two arguments: type (over, click, reset) and value. data-snippet-id-option becomes data-snippet-id. Several xml options can use the same data-snippet-id.

add a new gallery snippet

convert website_sale to the new option system