Table: implementation of Quasar's Qtable element

[dclause]

This is a second implementation proposition after the PR of @Diegiwg at https://github.com/zauberzeug/nicegui/pull/434

The current implementation is based on his, but allow more use cases and is more simple (IMO).

It allows:

• table selection
• table filter
• usage of table slots

The PR provide a basic example in the API reference page, as well as a more detailled example on how to use the table element with slots.

NOTE: It could be completed with some really nice to have scenarios like tables with icons, buttons and anything in rows if we could use props in slots. (see issue https://github.com/zauberzeug/nicegui/issues/501)