Feature/button block (#119)
* WIP add new button block type, that accepts text and url attributes
* style and fix bugs in the button block, streamlined delete block logic in input affiliated blocks, and fixed bug in which BlockCommandBar was being called twice
* autofocused the button block text input and cleaned up some stray console logs
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Co-authored-by: Brendan Schlagel <brendan.schlagel@gmail.com>
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