Add Flipper Doctor Component

Summary:
As designed by Vince [here](https://www.figma.com/file/4e6BMdm2SuZ1L7FSuOPQVC/Flipper?node-id=585%3A127550), this diff adds Flipper Doctor into Sandy

Note:
- The dot on Doctor icon will act similarly to `DoctorBar`
- add type to `count` for `LeftRailButton` to act like dot badge
- Get rid of padding in `antd` modal

Reviewed By: nikoant, mweststrate

Differential Revision: D24137349

fbshipit-source-id: 8ce441e0ed96083eba09d98dfd3a45ff9b5be027

desktop/themes/base.less

@@ -18,6 +18,12 @@
 @code-family: 'SFMono-Regular', Consolas, 'Liberation Mono', Menlo, Courier,
   monospace;
 
+/**
+  This section adds specific paddings to ANT component to match design
+*/
+@collapse-header-padding: 0;
+@collapse-content-padding: 0;
+
 /**
  This section maps theme base colors as defined in light/dark.less to ANT variables
  (as far as they aren't already)