v0.9.10

Lots of changes and updates here! This release represents a few months of bug fixes, optimizations, and a few new features, and is hopefully as stable as ever. Here's a list of some of the changes:

• Add a random screensaver picker, as well as basic 'system
  screensaver' support -- ie, screensavers that are integral to the
  application and not installed as a separate package.
• If 'Run Now' chosen in menu, don't check power state
• Improve dock display -- show icon for more windows and hide only
  when all windows are closed
• Tweak layout of prefs window and the preview tool
• Update main process to listen for events from windows and pass data
  around. The main process has responsibilty for opening windows,
  saving new screensavers, etc.
• Reorganize code for app, switch to a single package.json
• Make a bunch of calls asychronous
• Use async/await in a few places
• Add some data caching to help performance
• When launching screensavers, don't take screengrab unless
  requested - this greatly speeds up launch time
• Switch to yarn, cleanup build process
  • I'd prefer to not have yarn as a dependency, but it does a better
    job of handling installations across multiple platforms -- ie,
    windows and OSX
• Add webpack and use it to build UI assets
  • I also might get rid of this at some point, and also React for
    that matter
• Update bootstrap version and assorted styling
• Update electron version
• Update React version and a bunch of assorted components
• Add mocha tests
• Add appveyor and Travis builds
• Update some stale packages, and remove some dead ones