[Android] [PATCH] UI/UX: Replace checkboxes to on/off switches

[Alexey Rodionov]

> Why?

To avoid inconsistencies in UI (you have used on/off switch for
"Enable the black theme" setting only and checkboxes for all other
settings) and better compliance to Google material design guidelines
(checkboxes are designed to select multiple options from a set, and
on/off switches are designed to toggle the state of setting options).