Crumble UI touchups

[DeDuckProject]

Made some Crumble UI touchups:

• Fixed canvas blurriness which occurs on Retina display (and probably others)
• example circuits open as modal instead of inline (closes by esc/outside-click/clicking the "x")
• html style extracted to <style> tag - still inside the html file to ensure file is self-contained.
• Small improvements to layout (mainly buttons layout)
• main canvas size now dynamically calculated to fit screen (so no more scroll)

After:

Before:

[Strilanc]

I like the retina fixes and the dialog for the example circuits. But the other style changes seem sorta superfluous and appear to be breaking single-file-ness.

(Does hitting escape work for closing the dialog?)

[DeDuckProject]

I like the retina fixes and the dialog for the example circuits. But the other style changes seem sorta superfluous and appear to be breaking single-file-ness.

(Does hitting escape work for closing the dialog?)

I like the escape idea - will implement that + inline styles and revert the button opinionated styling.

[DeDuckProject]

@Strilanc, I took care of your comments and can merge as far as I'm concerened.
In particular:

• 'esc' closes dialog
• Brought back CSS into html file, but in a <style> tag, for better separation of concerns
• Removed opinionated styling for buttons, but left the layout (see updated screenshot in the PR description)
• Fixed an issue where opening "import/export" temporarily changed the proportions of the canvas until closing it. Note, we are now calling "applyDevicePixelScaling" from multiple places (when resizing screen, when opening import/export..). Alternatively, we can just listen to the resize of the canvas itself, and handle that in a single place - the issue is that the entire canvas flickers upon resize, so I can add throttling, but I feel all this might be over-engineering and we might as well leave it at that. If you think we should go there - let me know; otherwise let's merge this.

[Strilanc]

LGTM, I'll get it merged. Thanks!