improve page header

- optimize SVGs powered-by.svg and existdb-web.svg using SVGO
- use optimized SVGs in footer and header
- remove blurry gif from header
- remove header.gif
- remove existdb.png

src/main/xar-resources/resources/css/exist.css

@@ -170,11 +170,10 @@ body {
     position: relative;
   }
   #header {
-    background: #f3f3f3 url(../images/header.gif) top right no-repeat;
     width: 100%;
   }
   #header a#logo {
-    background: url(../images/existdb.png) center left no-repeat;
+    background: url(../images/existdb-web.svg) center left no-repeat;
     display: block;
     width: 220px;
     height: 100px;
@@ -199,15 +198,6 @@ body {
 #content {
   min-height: 600px;
 }
-#sourceforge {
-  background: url(../images/sourceforge.gif) no-repeat 50%;
-  width: 130px;
-  height: 30px;
-  display: block;
-  margin: 30px auto;
-  text-indent: -999em;
-  overflow: hidden;
-}
 #footer {
   clear: both;
   margin: 0 auto;
@@ -415,19 +405,6 @@ a:hover {
   padding: 3px;
   margin: 3px;
 }
-.code {
-  font: 14px/20px "Ubuntu Mono", Menlo, Consolas, "Courier New", Courier,
-    monospace;
-  background: #444444 url(../images/noise.png);
-  padding: 8.5px;
-  width: 100%;
-  margin: 18px 0 18px;
-  overflow-x: auto;
-}
-.code a {
-  padding: 4px;
-  border: 1px solid #c7c7c7;
-}
 figure img {
   display: block;
 }