WIP: Renderjs ui minimal theme

This bt5 provides a new web theme mimicking the style of erp5_web_renderjs_ui.

For exemple, by creating a web section using the new RJSStaticTheme skin selection like this :

it would render the dialog ERP5Site_viewCredentialRecoveryLoginDialog, that usually looks like this :

like this :

or like this on smaller screens :

The dialog submission works as expected. The goal would be to support as much features as possible of xhtml_style and / or erp5_web_renderjs_ui like portal status messages (maybe it does, I didn't try yet).