depviz.svg: Add a depviz logo

Discussion in [1].  This logo is my suggested simplicification of
Juan's DepCard-icon idea.

I also reduce the short-card relatedX offset to avoid exposing a bit
of the card border between the top and bottom DepIndicators.  That
makes the numbers more crowded as you get double-digit indicators, but
they aren't too bad.

[1]: jbenet#14

webapp/src/DepIndicators.js

@@ -58,7 +58,7 @@ class DepIndicators extends PureComponent {
   render() {
     var relatedX = this.props.cx;
     if (this.props.dy < 1.75) {
-      relatedX += 1;
+      relatedX += 0.6;
     }
     return <g className="DepIndicators">
       <DependenciesIndicator

webapp/src/Layout.css

@@ -1,20 +1,9 @@
 .Layout-header {
   background-color: #222;
   color: white;
-}
-
-.Layout-header h1 {
-  display: inline;
-  font-size: large;
-  height: 40px; /* sync with .Layout-logo and HeaderHeight */
-}
-
-.Layout-header a {
-  text-decoration: none;
-  color: white;
+	padding: 2px; /* sync with HeaderHeight */
 }
 
 .Layout-logo {
-  height: 40px; /* sync with .Layout-h1 and HeaderHeight */
-  vertical-align: middle;
+  height: 36px; /* sync with HeaderHeight */
 }

webapp/src/Layout.js

@@ -1,19 +1,18 @@
 import React, { Component } from 'react';
 import { Link } from 'react-router'
-import logo from './logo/react.svg';
+import logo from './logo/depviz.svg';
 import './Layout.css';
 
-/* sync with CSS .Layout-logo and .Layout h1 height. */
+/* sync with CSS .Layout-header padding and .Layout-logo height. */
 export const HeaderHeight = 40;
 
 class Layout extends Component {
   render() {
     return <div className="Layout">
       <div className="Layout-header">
-        <a href="https://github.com/jbenet/depviz">
-          <img src={logo} className="Layout-logo" alt="logo" />
-        </a>
-        <h1><Link to="/">depviz</Link></h1>
+        <Link to="/">
+          <img src={logo} className="Layout-logo" alt="logo (homepage)" />
+        </Link>
       </div>
       {this.props.children}
     </div>