fix #226 by using a colored "dot" instead of background color
NOTE: For a full fix, some changes need to be done to the Popover components theming (adding a border or shadow, see ubports/development/core/lomiri-ui-toolkit#37). As agreed upon in UX group, this MR is not going to add this for calendar app only.
This MR does provide a fix for the sometimes unreadable all day event labels. To fix this, a couple of changes will be applied:
- instead of a fully colored background, a colored "dot" is used
- the popover margins at top and bottom are removed
- instead of a rectangle a ListItem is used for the delegate
- the label is aligned left
- the label does elide right so long labels do not overprint the popovers edges and the "dot"
Screenshots: