Add basic trace context management

[tahini]

That means when we navigate a trace, it saves the current context: visible time range, selection, opened views, the visible entries in each view, etc. Context can be shared, i.e. we can copy paste some kind of url that we can send to a colleague to see the same “view” of the system.

Note that the trace server itself is stateless, so the context data should be saved in the theia server backend.

• Develop the classes to save the current context stack
• Time ranges and current outputs are a good first start for the context
• As the user navigate, save a stack of the current context
• Add the whole context to the copy-paste URL of a trace, so the person who will open the link will directly arrive at the same context
• Save the "state" of the frontend to not lose the current work when you refresh the browser
• Add the possibility to undo/redo. Find some key binding (ctrl-z/ctrl-y in a browser? Some other standard for that kind of application?) and stack/unstack contexts to go back to previous context
• Look if there are any browser standard fro that kind of context: for example snowflake
• Test that all actions supposed to change the context do so correctly and can be done/undone