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/theme.tsx

@@ -0,0 +1,60 @@
+import { createMuiTheme } from '@material-ui/core/styles';
+
+declare module '@material-ui/core/styles/createPalette' {
+  interface TypeBackground {
+    appBar: string
+  }
+}
+
+export const lightTheme = createMuiTheme({
+    palette: {
+      type: "light",
+      background: {
+        default: '#fafafa',
+      },
+      primary: {
+        main: '#6a6a6a',
+      },
+      secondary: {
+        main: '#333333',
+      },
+    },
+    typography: {
+      fontFamily: [
+        'Work Sans',
+        'Montserrat',
+        'Nunito',
+        'Roboto',
+        '"Helvetica Neue"',
+        'Arial',
+        'sans-serif'
+      ].join(','),
+    }
+});
+  
+export const darkTheme = createMuiTheme({
+    palette: {
+      type: "dark",
+      background: {
+        default: '#0d1117',
+        paper: '#161b22',
+      },
+      primary: {
+        main: '#dd7700',
+      },
+      secondary: {
+        main: '#1f2937',
+      },
+    },
+    typography: {
+      fontFamily: [
+        'Work Sans',
+        'Montserrat',
+        'Nunito',
+        'Roboto',
+        '"Helvetica Neue"',
+        'Arial',
+        'sans-serif'
+      ].join(','),
+    }
+});