Decide if we really need two slots on the wrapper component

[0gust1]

The wrapper component actually has 2 slots: inside and outside.

The reason is mostly to offer the user enough options to place its own components around the molstar <canvas>.
Typically, the inside slot would be useful for any UI element that should be placed "over" the molstar canvas (the parent has a position:relative CSS behavior.

But in fact those two slot may complexify the API for the user. Further tests with various layouts are needed.