instantiate only `AutoUi` with `schema`

[jgunstone]

currently everything must be instantiated with schema which doesn't make much sense... e.g.

• AutoArray must be an array:
• EditGrid must be an array
• AutoObject must be an object .. etc. so they should be instantiated with what makes sense for the them - ie..
• AutoArray- items
• EditGrid - items
• AutoObject - properties

• AutoUi is the top level - in doesn't care what it generates, so this should still be instantiated with schema. probably makes sense to add a .from_schema method to the other objects to ease transition...

[jgunstone]

instead of instantiating with schema use AutoArray (**kwargs) and ensure that the class has the correct traits i.e.

• AutoObject requires properties trait
• AutoArray requires items trait

[jgunstone]

merged to main in this PR https://github.com/maxfordham/ipyautoui/pull/199