Add scripts to update+run Dashboard, Pegasus and Blockly-dev with a single command.

Added features:
- Single command (`./up`) to run Dashboard, Pegasus, and Blockly servers in development mode.
- Manage all three subprojects from a single startup/shutdown point.
- Automatically make sure system dependencies/migrations are all up-to-date before launching a project (no more forgetting to run `bundle install`, `npm update` or `bundle exec rake seed:all` after an update).