Feature/zen mode (#110)

* Start with implementation
* Refactor AuthGuard, persist displayMode in user settings
* Refactor DisplayMode to ViewMode
* Update changelog

prisma/schema.prisma

@@ -92,10 +92,11 @@ model Property {
 }
 
 model Settings {
-  currency  Currency
-  updatedAt DateTime @updatedAt
-  User      User     @relation(fields: [userId], references: [id])
-  userId    String   @id
+  currency  Currency?
+  viewMode  ViewMode?
+  updatedAt DateTime  @updatedAt
+  User      User      @relation(fields: [userId], references: [id])
+  userId    String    @id
 }
 
 model User {
@@ -133,6 +134,11 @@ enum DataSource {
   YAHOO
 }
 
+enum ViewMode {
+  DEFAULT
+  ZEN
+}
+
 enum Provider {
   ANONYMOUS
   GOOGLE