use more subtle progress when reloading

[devoncarew]

Use more subtle progress when reloading:

• introduce a 3rd compiling state (none, compiling, and compiling as part of a reload)
• when reloading, use 'Reloading...' as the text in the editor progress message
• when reloading, don't display a semi-opaque overlay over the execution area (this makes the reload update appear too heavy-weight)

There's likely some follow up wrt the run/reload buttons (we probably want to overload run for reload, perhaps change the button text depending on what would happen when you hit it, and slightly deemphasize the 'restart' button).

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