feat: various UI improvements (#36)

* fix: content offset

When the appbar was changed to a `div` the content became offset, this fixes that.

* style: make display of cheques table more readable

* style: restyle sidebar

* fix: content overflow

* chore: split theme into separate file

* feat: show ethereum transaction link for cashout

* feat: make cashout link to etherscan transaction

Co-authored-by: Vojtech Simetka <vojtech@simetka.cz>

src/components/SideBar.tsx

@@ -68,6 +68,7 @@ const useStyles = makeStyles((theme: Theme) =>
     },
     activeSideBarItem: {
       borderLeft: '4px solid #dd7700',
+      backgroundColor: 'inherit !important'
     },
     toolbar: theme.mixins.toolbar,
   }),