Incorrect tab state when not using `id` on Tabs and/or reusing `value` on nested dcc.Tab

[Marc-Andre-Rivet]

Original community issue: https://community.plot.ly/t/tabs-of-tabs-has-odd-behavior/19577

Expected resolution:

• tabs without an explicitly provided id act normally (probably by generating an id on the fly)
• test demonstrating that tabs without id behave as expected
• test demonstrating that tab value sharing between different tabs is not problematic

There also seems to be a problem retaining the previous of a tab -- a tab with a nested tabs will lose the selected nested tab when switched out and in again.