Focus Element system

[LuanRoger]

This system will be used to get the last valid focused element.
The focused element can store an Object value.

The valid element just need to be focable, but not all element need to update the object.
This value need to have a timeout to be cleared.

Motivation

The stored value will use to get the games information to be used in context menu on My Games section.

TODO

• Expose the focus from custom widgets #29

[LuanRoger]

• Done in 5b4252b

Not every element supports the focus for now, this progress will be tracked on #29