Rename page to Manage Tasks

Trying to align terminology with the docs

ui/src/kapacitor/components/KapacitorRules.js

@@ -109,7 +109,7 @@ const PageContents = ({children}) =>
     <div className="page-header">
       <div className="page-header__container">
         <div className="page-header__left">
-          <h1 className="page-header__title">Manage Alerts</h1>
+          <h1 className="page-header__title">Manage Tasks</h1>
         </div>
         <div className="page-header__right">
           <SourceIndicator />

ui/src/side_nav/containers/SideNav.js

@@ -121,7 +121,7 @@ const SideNav = React.createClass({
             <NavHeader link={`${sourcePrefix}/alerts`} title="Alerting" />
             <NavListItem link={`${sourcePrefix}/alerts`}>History</NavListItem>
             <NavListItem link={`${sourcePrefix}/alert-rules`}>
-              Manage Alerts
+              Manage Tasks
             </NavListItem>
           </NavBlock>