Some ideas for a rework of getting started form

Hi,

These are some ideas for a rework of the UX of the getting started screen.

Main ideas are:

• To have a more welcoming message, emphasing that this is your Kresus, that it is personal etc.
• Move the advanced options tab to a dedicated subsection of the form. Having it next to "Configure a new bank access" and "Import" was a bit misleading in my opinion, as it was easy to miss it by considering it as yet another source of credentials.
• Replace the long select list by an input with autocomplete.
• Add options to add a default set of categories (#39 (closed)) and a default set of alerts. Checked by default as most people will likely want to know about this feature and try it upon installation.
• Move Weboob options in a dedicated sub panel, folded by default.
• Add a button to start in a so-called "demo mode" (eventually with an alert/popover giving more infos).

This is just a simple mock up for now, to share some ideas. Let me know what you think about it, and what could be totally wrong :)

This fixes #648 (closed), #627 (closed) , #483 (closed) and #39 (closed).