- use postMessage api instead of dispatching custom events on canvas wrapper element
- add actualChrLocation field to browser location state
  (shows where the browser is at any given moment)
- add message counter that keeps track of the sequence of messages
  exchanged between GenomeBrowser and BrowserChrome.
- move code for updating GenomeBrowser page url from Browser component to browserActions
- update .gitignore rules regarding .vscode folder