Replace title attribute

[bjuppa]

This PR cleans up usage of the title html attribute that causes duplications in many screenreaders, and also it's not an accessible way to get a "tooltip".

For links, the name and description are now combined into aria-label, unless every word in name is already present in description, if so only description is used to avoid duplication.

The description is put into data-kontour-description and styling is also updated to display it as a tooltip when a link is hovered, focused or active.

In addition the data-kontour-username is displayed as a tooltip on top for recent team links in the widget. Before this was only in attribute and never displayed visually in the interface.

This PR contains breaking changes:

• New method getLabel() on the AdminLink contract
• Removes $description for button Blade templates, so anyone using them needs to change it to aria-label for same behaviour.

Closes #145

[bjuppa]

Ok, I'm going to change direction here one more time 😆

• [x] I'll use data-kontour-description in addition to aria-label and the CSS will take the description for the "tooltips".
• [x] I will write some sass placeholders for tooltip styling (top and bottom variants).
• [x] Also, now that I removed title from buttons, perhaps we should put something like $controlAttributes in there so buttons can be extended (This one needs some thinking as it may be easier to just write the html directly instead of pulling in a blade include). Edit: This is already handled by $buttonAttributes!