Underline links in Help panel and fix /docs/help in browser extensions

Underline links in the Help panel text to make them standout and make
the `/docs/help` URL work when the app is served from browser extensions
extension by prefixing it with the service URL.

Also remove extraneous spaces from around the 'Send us a message' text.

h/static/scripts/directive/help-panel.js

@@ -15,6 +15,7 @@ module.exports = function () {
       this.userAgent = $window.navigator.userAgent;
       this.version = settings.release;
       this.dateTime = new Date();
+      this.serviceUrl = settings.serviceUrl;
 
       $scope.$watchCollection(
         function () {

h/static/styles/help-panel.scss

@@ -38,6 +38,7 @@
 
 .help-panel-content__link {
   color: $grey-6;
+  text-decoration: underline;
   &:hover {
     text-decoration: underline;
   }

h/templates/client/help_link.html

 
-  <a class="help-panel-content__link" href="mailto:support@hypothes.is?subject=Hypothesis%20support&amp;body=Version:%20{{ vm.version }}%0D%0AUser%20Agent:%20{{vm.userAgent}}%0D%0AURL:%20{{ vm.url }}%0D%0APDF%20fingerprint:%20{{ vm.documentFingerprint ? vm.documentFingerprint : '-' }}%0D%0AUsername:%20{{ vm.auth.username ? vm.auth.username : '-' }}%0D%0ADate:%20{{ vm.dateTime | date:'dd MMM yyyy HH:mm:ss Z' }} ">
-    Send us a message 
-  </a>
-
+<a class="help-panel-content__link"
+   href="mailto:support@hypothes.is?subject=Hypothesis%20support&amp;body=Version:%20{{ vm.version }}%0D%0AUser%20Agent:%20{{vm.userAgent}}%0D%0AURL:%20{{ vm.url }}%0D%0APDF%20fingerprint:%20{{ vm.documentFingerprint ? vm.documentFingerprint : '-' }}%0D%0AUsername:%20{{ vm.auth.username ? vm.auth.username : '-' }}%0D%0ADate:%20{{ vm.dateTime | date:'dd MMM yyyy HH:mm:ss Z' }} "
+>Send us a message</a>

h/templates/client/help_panel.html

@@ -15,9 +15,9 @@
       document-fingerprint="vm.documentFingerprint"
       auth="vm.auth"
       date-time="vm.dateTime">
-    </help-link>  
-    if you have any questions or want to give us feedback. 
-    You can also visit our <a class="help-panel-content__link" href="/docs/help" target="_blank"> help documents.</a>
+    </help-link>
+    if you have any questions or want to give us feedback.
+    You can also visit our <a class="help-panel-content__link" href="{{vm.serviceUrl}}docs/help" target="_blank"> help documents</a>.
   </div>
   <header class="help-panel-title">
     About this version