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/index.css

@@ -1,4 +1,6 @@
 body {
+  height: 100vh;
+  min-height: 100vh;
   margin: 0;
   font-family: 'Work Sans', -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', 'Oxygen',
     'Ubuntu', 'Cantarell', 'Fira Sans', 'Droid Sans', 'Helvetica Neue',
@@ -7,6 +9,12 @@ body {
   -moz-osx-font-smoothing: grayscale;
 }
 
+#root {
+  height: 100%;
+  min-height: 100%;
+  overflow-y: auto !important;
+}
+
 code {
   font-family: source-code-pro, Menlo, Monaco, Consolas, 'Courier New',
     monospace;