Only Render Histogram if you Can

[jameskerr]

Hello!

These changes will improve a few things.

1. If there is no pool name present in the query, this histogram will not render.
2. If you press Cmd+L (on macOS) or Ctrl+L (on Linux/Windows), the editor will receive focus.
3. If you switch tabs to a query session, the editor will receive focus automatically.

fixes #3093

[philrz]

I tested out the branch and it's a functional 👍 for me.

As would be expected, the Cmd+L behavior on macOS worked as Ctrl+L on Linux, so I updated the PR text to reflect that's expected. Also, while the "focus automatically" sounds like what we want, I banged on some older releases and in everything I tried the cursor always landed in the editor as soon as I selected a tab with a Query Session anyway. But if these changes make it extra certain that'll happen a la "belt & suspenders", I'm all about it. 😄