Implement a worker for batch exporting of usage logs

This will allow customers to request their usage logs for a repository or an entire namespace, and we can export the logs in a manner that doesn't absolutely destroy the database, with every step along the way timed.

static/directives/logs-view.html

@@ -23,6 +23,8 @@
     <span class="hidden-xs right">
       <i class="fa fa-bar-chart-o toggle-icon" ng-class="chartVisible ? 'active' : ''"
          ng-click="toggleChart()" data-title="Toggle Chart" bs-tooltip="tooltip.title"></i>
+      <button class="btn btn-default download-btn" ng-click="showExportLogs()"
+              ng-if="user || organization || repository"><i class="fa fa-download"></i>Export Logs</button>
     </span>
   </div>
 
@@ -98,4 +100,27 @@
       <div class="cor-loader" ng-show="loading"></div>
     </div>
   </div>
+
+  <!-- Modal Dialog -->
+  <div class="cor-confirm-dialog"
+       dialog-context="exportLogsInfo"
+       dialog-action="exportLogs(exportLogsInfo, callback)"
+       dialog-title="Export Usage Logs"
+       dialog-action-title="Start Logs Export"
+       dialog-form="context.exportform">
+      <form name="context.exportform">
+        <div style="margin-bottom: 14px;">
+          Enter an e-mail address or callback URL (must start with <code>http://</code> or <code>https://</code>)
+          at which to receive the exported logs once they have been fully processed:
+        </div>
+        <input class="form-control" type="text" ng-model="exportLogsInfo.urlOrEmail"
+               placeholder="E-mail address or callback URL"
+              ng-pattern="'(http(s)?:.+)|.+@.+'">
+        <div class="help-text">
+          Note: The export process can take <strong>up to an hour</strong> to process if there are many logs. As well,
+          only a <strong>single</strong> export process can run at a time for each namespace. Additional export requests will be
+          queued.
+        </div>
+      </form>
+  </div>
 </div>