Cursor blinking rate configuration

Hello and thanks a lot for great project!

**Is your feature request related to a problem? Please describe.**
I'm always frustrated by frequently blinking cursor, I've set rate to minimum in my Windows setting, but site uses it's own cursor. On Firefox with default high contrast (HC) mode blinking also leads to visual issue: the character right from selection gets blank on blinking, due to dark color. For now, I use to click (set focus) out of editor when I'm not writing.

**Describe the solution you'd like**
Add setting for cursor blinking rate.

**Describe alternatives you've considered**
Use system's cursor or only rate.

**Additional context**
[Visual Issue in HC mode](https://user-images.githubusercontent.com/49620111/131384205-cb950129-5b9c-4e30-bad6-2a21df02562d.png)

Thanks.