Auto-update

Auto-update using Esky wrapper around py2app, py2exe.
* Souma checks for updates during startup and every 15 minutes, downloads them and applies at next restart.
* Update list is fetched from Github Wiki.

Changes:
* Startup is no longer prevented if the database is outdated to allow for testing.
* Version identifier must be in `major.minor.patch` format, no appendixes (e.g. `-alpha.1`).
* Startup is much quicker now, since Synapses are only initialized after web_ui is started