feat: load themes dynamically

ui/src/themes/dark.js

@@ -1,6 +1,7 @@
 import blue from '@material-ui/core/colors/blue'
 
 export default {
+  name: 'Dark (default)',
   palette: {
     primary: {
       main: '#90caf9'

ui/src/themes/index.js

@@ -1,4 +1,4 @@
 import LightTheme from './light'
 import DarkTheme from './dark'
 
-export { LightTheme, DarkTheme }
+export default { LightTheme, DarkTheme }

ui/src/themes/light.js

@@ -1,4 +1,5 @@
 export default {
+  name: 'Light',
   palette: {
     secondary: {
       light: '#5f5fc4',