defer canvas creation

[jerch]

Should fix #55.

[jerch]

@Tyriar This PR should remove most of the nasty init burden and initialize the canvas & the placeholder lazy. This is not the nicest PR, but gets the job done in local tests. For normal terminal usage w'o any image sequences there should not be any image canvas anymore on the DOM.

Not quite sure how you can test it without going through the whole build burden (the bootstrapping is quite cumbersome I admit) - I can do a local bundle and put the file in a gist for testing, if you want.

Edit: The changes are not that much, thus I dont mind transferring them myself.

[jerch]

@Tyriar The Pr is done. The changes got bigger than anticipated 😸 , whatever - gonna do a last patch release for these here, and apply the code changes in the base repo PR afterwards.