* Remove squirrel hooks (the installing & uninstalling is now
done by the, er, installer)
* Switch to electron-auto-update
* Shorten initial update delay because we no longer need to wait
for squirrel to release a lock file
* Change update URLs because windows is now one installer for
both 32 & 64 bit.
* Update electron-builder to 10 where NSIS is now the default
target for Windows.
* Add linux to the target list, building a deb.
* Remove sqirrel-specific installation spinner
* Remove redundant !**/* from files
David Baker