Make the behavior with workspace tabs the same as Dynamo's one

- disable removing `Home` workspace;
- disable having more than one `Home` workspace;
- disable editing workspace name;
- set custom node workspace name from a dialog, `Home` workspace name should be "Home".

It would be better to merge first:
- https://github.com/pboyer/flood/pull/64 (without this changes opening won't work at all);
- https://github.com/pboyer/flood/pull/65 (with this changes tab name will be updated by file name).