Add: Focus mode

[minthemiddle]

To add an optional focus mode that can be toggled on and off.

[minthemiddle]

I'll break down the features one by one.
Focus mode is more of a milestone than a feature.

[minthemiddle]

I'm keeping this issue to capture high level thoughts about this release.

[minthemiddle]

Will be the first release with early beta releases.
First version will be v1.10.0-beta.1 (see here)

[minthemiddle]

All features will initially be tied to "focus" mode which gets toggled via cmd+f key shortcut.