Explorer: Add block/kernel search field (#1991)

* Explorer: Allow querying all node args through URL

- Use same query 'types' in URL as in node query.
- Add the "treasury" as a pseudo-type in URL (just for convenience).
- Make all arguments into global variables that can be used in URL.
- Add error messages for blocks & kernels not found.
- Display Genesis block (instead of Treasury) by default for "block" query without specific height nor kernel.
- Highlight the queried kernel in block details.

* Explorer: Add block/kernel search

* Explorer: merge AddClass and AddClassEx