Some fixes in rendering legacy plugins

Summary:
Some exploratory testing on all iOS and Android plugins, to see how they behave inside Sandy, and fixed some layout glitches (some were also present without Sandy)

General fixes:
* Introduced some niceties like searchbox resizing properly, and toolbars wrapping automatically in Sandy, rather than buttons becoming invisible
* Containers don't grow anymore by default, but take size of contents
* ScrollContainer child is now a Layout.Vertical. Layout.Vertical should be used as default container everywhere (e.g. Tabs, Panels) in the future
* Fixed layout issue if a split container had only 1 visible child
* DetailsSidebar now scrolls vertically by default
* Details sidebar would sometimes render content in-place rather than in the reserved area
* AppSelector dropdown and Plugin list will now properly ellipse (...) if there is not enough space

Plugin fixes:
* Long database / table names in Database plugin would break layout

Also fixes https://github.com/facebook/flipper/issues/1611

Reviewed By: passy

Differential Revision: D24454188

fbshipit-source-id: c60c867270900a1d4f28587d47067c6ec1072ede

desktop/app/src/ui/components/Tabs.tsx

@@ -104,6 +104,7 @@ const TabContent = styled.div({
   height: '100%',
   overflow: 'auto',
   width: '100%',
+  display: 'flex',
 });
 TabContent.displayName = 'Tabs:TabContent';