TopBar fixes

[alepev]

• Add config option to enable showing TopBar in OTG
• Fix bug that causes TopBar to overlap with the search box at the top of the page when you click on it to search a term (only when TopBar is active, i.e. configShowTopBar = true) - both OTG & OTP

[alepev]

As I said in person I could be nitpicky about making the commit message headline more about what it achieves rather than the ‘how’ (which is already reflected in the code/comments), but we can probably squash all the top bar commits into one patch when rebasing to future releases anyway. And for the content of the code, we pair-programmed on that and agreed that the other options (single-points of truth for config access and height of the top bar as well as potentially avoiding deprecated styling code that the rest of the app still uses) didn't look worth the effort for now. Looks good to me.

I suggest to leave the other commit message as is since we agree it should be squashed, but I will try to do better with future ones :)