Make sure Ansible playbook runs through on vagrant up.

Variables in development_hosts are not passed to Ansible when it
is called by Vagrant. This commit uses ansible.extra_vars to
explicitly pass development arguments on vagrant up.
Setup uWSGI to run at startup.

We will use uWSGI to run our app both in development and production.
uWSGI is run in Emperor mode for simplicity in configuration and set
to run on startup with Upstart.
Hardcode appserver to be run as www-data.

For some reason sudo_user can't read from hostvars and groupvars
but able to substitute from extra_vars. This commit removes ability
to user running user and enforce the app to be run as www-data.
Setup application configuration files via Ansible.

In order to ensure they're updated alongside with server provisioning
its configuration is now being managed by Ansible instead of a static
file in the application directory.
Rename webservers groups to all.yml.

Use group_vars/all.yml to define default configurations so we could override
it when needed.