Add icons to the theme (level icons + VR icon)

[hugoattal]

I should update those icons:

• [x] VR Buttons
• [x] Material Editor
• [x] Mesh Editor
• [x] Animation Editor

Done

    

[GoVRCenter]

The VR mode too please! Thanks so much, loving the plugin.

[hugoattal]

It's getting somewhere!

Still have to do the small version though 😅...

EDIT: done

[hugoattal]

The animation editor:

EDIT: and the small version:

[hugoattal]

I'll do the small ones in another issue for the 1.7, I'm marking this as ready for 1.6.