Improve navbar menu styling and add options for icon use

[Manoj Solanki]

Improve the styling of the navbar menu.

Consider making sub-menus not have rounded corners, or offer it as an option if possible

Add 3 styling options for:

1. Show menu with icons
2. Show menu without icons, show down facing arrow for sub-menus
3. None

Also make the sub-menus render smoothly with animation to look slicker.

[Manoj Solanki]

Add new navbar styling section. Add option for border radius for dropdown menus in there and the others above.

[Manoj Solanki]

Added border radius option and new navbar styling section here. https://bitbucket.org/covuni/moodle-theme_adaptable/commits/de47759a306cb183dd5232180f1298191f2987eb

[Manoj Solanki]

Add smooth rendering to menu here. https://bitbucket.org/covuni/moodle-theme_adaptable/commits/819215f85caba10240a5162f7d31c192f2645ede

[Manoj Solanki]

Fix #896. Final changes. This adds options for displaying the icons and submenu arrow

→ <<cset 2ac43491b9e8>>