Exclude Trending reports from Dashboard widgets.

Changed code to exclude Trending reports from widget editor because those are not like regular reports and do not have columns. Show a message instead of third pull-down "No Reports to select" in the view.

https://bugzilla.redhat.com/show_bug.cgi?id=1163952
Refactored code in schedule_menus method.

- Renamed schedule_menus method to report_selection_menus, and changed all it's callers.
- Moved report_selection_menus method to reports controller, as it is a common method schedules and widgets editor.
- Added spec tests for report_selection_menus method
- Changed message to be displayed for folders that do not have reports .

https://bugzilla.redhat.com/show_bug.cgi?id=1163952
Converted view to haml.

- Used gettext to display "No Widget compatible Reports found" message.

https://bugzilla.redhat.com/show_bug.cgi?id=1163952
Merge pull request #1115 from h-kataria/exclude_trending_reports_in_dashboard_widget_editor

Exclude trending reports in dashboard widget editor