Get Gatsby to parse the docs

This isn't having Gatsby do anything with the docs yet, it's just getting
it to load the docs without complaining.

 - Use the `gatsby-source-filesystem` and `gatsby-plugin-mdx` plugins to
   load the docs.
     + It turns out that various JS files in the docs import a bunch of
       third-party modules, so add those in `package.json`.
 - Adjust the docs to use an "@src" alias instead of a bunch of "../"
   sequences, to avoid the docs needing to know where they are subtree'd
   in at.  This alias is configured in `gatsby-node.js`.
 - Copy some JS-imported resources from getambassador.io.git:
    + Some images (`src/assets/icons/*.svg`)
    + Some CSS (`src/components/Layout/vars.less`)
 - Add a trivial MVP of the JS-imported <CodeBlock> component, rather than
   figuring out what all of the etambassador.io.git <CodeBlock>'s
   dependencies are in order to copy it.

Signed-off-by: Luke Shumaker <lukeshu@datawire.io>

install/old-version-tabs.js

@@ -5,9 +5,9 @@ import AppBar from '@material-ui/core/AppBar';
 import Tabs from '@material-ui/core/Tabs';
 import Tab from '@material-ui/core/Tab';
 import Box from '@material-ui/core/Box';
-import CodeBlock from '../../../../../src/components/CodeBlock';
-import LinuxIcon from '../../../../../src/assets/icons/linux.inline.svg';
-import AppleIcon from '../../../../../src/assets/icons/apple.inline.svg';
+import CodeBlock from '@src/components/CodeBlock';
+import LinuxIcon from '@src/assets/icons/linux.inline.svg';
+import AppleIcon from '@src/assets/icons/apple.inline.svg';
 
 function TabPanel(props) {
   const { children, value, index, ...other } = props;

quick-start/qs-tabs.js

@@ -6,10 +6,10 @@ import Tabs from '@material-ui/core/Tabs';
 import Tab from '@material-ui/core/Tab';
 import Box from '@material-ui/core/Box';
 import HubspotForm from 'react-hubspot-form';
-import CodeBlock from '../../../../../src/components/CodeBlock';
-import LinuxIcon from '../../../../../src/assets/icons/linux.inline.svg';
-import AppleIcon from '../../../../../src/assets/icons/apple.inline.svg';
-import WindowsIcon from '../../../../../src/assets/icons/windows.inline.svg';
+import CodeBlock from '@src/components/CodeBlock';
+import LinuxIcon from '@src/assets/icons/linux.inline.svg';
+import AppleIcon from '@src/assets/icons/apple.inline.svg';
+import WindowsIcon from '@src/assets/icons/windows.inline.svg';
 
 function TabPanel(props) {
   const { children, value, index, ...other } = props;

quick-start/telepresence-quickstart-landing.less

@@ -1,4 +1,4 @@
-@import '../../../../../src/components/Layout/vars.less';
+@import '~@src/components/Layout/vars.less';
 
 .doc-body .telepresence-quickstart-landing {
     font-family: @InterFont;