Use system highlight color instead of blue.

[rishig]

Chrome, Firefox, and Safari all seem to use the OS's default text highlight color, and we should as well. The current behavior looks pretty bad on stock Ubuntu, which uses orange as the highlight color.

To test on a Mac, I think the setting is System Preferences > General > Highlight Color. I haven't looked into where the setting is on other OSes.

Some discussion at https://chat.zulip.org/#narrow/stream/16-desktop/subject/orange.20vs.20blue.20highlight/.

[akashnimare]

We can try to add this using different types of available electron api but ideally, this should be added in the chromium itself. The issue exists in Chrome also - electron/electron#15068

[akashnimare]

Filed the bug in chromium - https://bugs.chromium.org/p/chromium/issues/detail?id=896189#c3.