[avatar] title attribute is inconsistent and depends on how properties are set

[Peppe]

The title (tooltip) behaviour changes depending if you set the properties declaratively or programmatically.

If you set the following:

<vaadin-avatar name="Joan Doe" abbr="JD"></vaadin-avatar>

Then the title will be set to "Joan Doe" in:
https://github.com/vaadin/vaadin-avatar/blob/master/src/vaadin-avatar.js#L234

If you set the following

<vaadin-avatar></vaadin-avatar>
avatar.name='Joan Doe';
avatar.abbr="JD"

Then the title is "Joan Doe (JD)" due to https://github.com/vaadin/vaadin-avatar/blob/master/src/vaadin-avatar.js#L291. Notice the abbreviation in parenthesis, which was missing in the previous case.

It shouldn't matter which way I put the properties, the end result should always be same. Also if I start declaratively and update it later programmatically, then the behaviour changes in the middle.