Update Ansible syntax in 'nginx' role

This patch fixes several logic errors in 'nginx' role tasks and updates
the syntax to be more streamlined. It also adds two variables:

- 'nginx_base_packages' defines a list of packages to install;
- 'nginx_privileged_group' defines a system group with privileged access
  to nginx (users in that group can create custom configuration files
  for nginx and reload nginx server using sudo), by default 'webadmins';
Re-enable nginx from wheezy-backports

A workaround to restart nginx server on first install seems to fix the
problem with missing pid in /var/run/nginx.pid.
Define 'nginx_local_servers' hash by default

This should make 'nginx' role a little faster to process (fewer skipped
tasks).
Rewrite default nginx server template

This rewrite cleans up default nginx server template and makes it
(hopefully) more readable. Important changes:

- 'item.name' variable has changed type from string to a list (almost
  all roles have been updated to use new type), first list entry is used
  as the "main" domain;
- 'item.location_list' has been added as an alternative 'location'
  configuration, which uses list of hashes to configure nginx locations.
  Bot variations can be used together, 'location_list' will be generated
  first. Examples are providied in defaults/main.yml;
Update CHANGELOG.md
Update python-crypto package on Travis-CI to 2.6.x
More updates on Travis-CI and quieter bootstrap
Switch Travis-CI build to Ansible v1.6.10

At the moment Ansible deb build seems to have problems with "missing
setuptools" which are installed seemingly correctly from Ubuntu 14.04
LTS. This is a test to see if stable Ansible build will work in new
environment.
Disable upgrade to Ubuntu 14.04 LTS on Travis-CI

Previous change didn't fix the build issue, so now time to check if
previous environment will do the trick, still on stable v1.6.10.
Switch Travis-CI build to Ansible v1.6.4

Ansible v1.6.10 builds but does not work with the playbook, let's try an
even older version. Just to commit latest changes and move on...
Install Ansible from official PPA on Travis-CI

Previous idea didn't work, let's try another one. This will use official
stable Ansible builds, maybe building from devel will be possible in the
future.
Fix wrong apt installation task in nginx

Lists of packages must be used with 'with_items', not directly, for
'apt' module to work.
Disable local APT repository on Travis-CI.

Ehh. At the moment on Travis-CI instance Ansible cannot download GPG
signing key for local repository. I'm not sure where the problem occurs
(probably nginx, since that was primarly what changed lately), so I want
to see the rest of the playbook.
Disable ginas and ansible roles on Travis-CI
Merge pull request #118 from drybjed/role/nginx

Updates in 'nginx' role, fixes for Travis-CI errors