notify defaults and feature updates

[kfarr]

Higher priority:

• default duration should be 6000 (6 seconds)
• font size should be increased to 18px
• maximum width of the notification should be increased to ~90% of viewport width before wrapping text

Lower priority:

• when the editor is open the notification should be above the help ? button if possible
• there is an error in position schema making it not possible to specify both x and y: the schema defines position as a "string" but then provides a default of an array of vec2 values, see https://aframe.io/docs/1.4.0/core/component.html#property-types

[kfarr]

done for now by #346