Set `$dashboard` in `DashboardPageController`

Set `$dashboard` in `DashboardPageController`

Avoid a fair amount of boilerplate in dashboard page views as almost all
of them contain
`Loader::helper('dashboard')->getDashboardPageHeaderWrapper()` etc
Merge pull request #108 from mkly/set_dashboard_helper_in_dashboard_page_controller

Set `$dashboard` in `DashboardPageController`