Fix dialog styles, remove context menu from ConversationListItem's dialogs

- Restore dialog styles that magically disappeared
- Fix font-family on ConfirmationDialog's content
- Remove the custom context menu that was appearing on dialogs

Change-Id: If828d5f6b3bdfc2a6e31c58fe40ad5fff286df3d
diff --git a/client/src/themes/Default.ts b/client/src/themes/Default.ts
index 0245b67..aceec0f 100644
--- a/client/src/themes/Default.ts
+++ b/client/src/themes/Default.ts
@@ -253,6 +253,38 @@
           },
         },
       },
+      MuiDialog: {
+        styleOverrides: {
+          paper: {
+            padding: '16px',
+            boxShadow: '3px 3px 7px #00000029',
+            borderRadius: '20px',
+          },
+        },
+      },
+      MuiDialogActions: {
+        styleOverrides: {
+          root: {
+            padding: '0px',
+          },
+        },
+      },
+      MuiDialogContent: {
+        styleOverrides: {
+          root: {
+            padding: '0px',
+            margin: '16px 0px',
+            minWidth: '500px',
+          },
+        },
+      },
+      MuiDialogTitle: {
+        styleOverrides: {
+          root: {
+            padding: '0px',
+          },
+        },
+      },
       MuiSwitch: {
         defaultProps: {
           disableRipple: true,