Connectivity & security directives

Added role variables (and sane defaults) for the following:

### Timeout
* Proposed ansible var: `apache_timeout`
* Proposed default value: `300`
* Distro default values:
  * debian 6: `300`
  * debian 7: `300`
  * ubuntu 12: `300`
  * ubuntu 14: `300`
  * centos 6: `60`

### KeepAlive
* Proposed ansible var: `apache_keepalive`
* Proposed default value: `On`
* Distro default values:
  * debian 6: `On`
  * debian 7: `On`
  * ubuntu 12: `On`
  * ubuntu 14: `On`
  * centos 6: `Off`

### KeepAliveTimeout
* Proposed ansible var: `apache_keepalive_timeout`
* Proposed default value: `15`
* Distro default values:
  * debian 6: `15`
  * debian 7: `5`
  * ubuntu 12: `5`
  * ubuntu 14: `5`
  * centos 6: `15`

### MaxKeepAliveRequests
* Proposed ansible var: `apache_max_keepalive_reqs `
* Proposed default value: `100`
* Distro default values:
  * debian 6: `100`
  * debian 7: `100`
  * ubuntu 12: `100`
  * ubuntu 14: `100`
  * centos 6: `100`

### ServerTokens
* Proposed ansible var: `apache_server_tokens `
* Possible values: `Full` | `OS` | `Minimal` | `Minor` | `Major` | `Prod`
* Proposed default value: `OS`
* Distro default values:
  * debian 6: `OS`
  * debian 7: `OS`
  * ubuntu 12: `OS`
  * ubuntu 14: `OS`
  * centos 6: `OS`

### ServerSignature
* Proposed ansible var: `apache_server_signature `
* Possible values: `On` | `Off` | `EMail`
* Proposed default value: `On`
* Distro default values:
  * debian 6: `On`
  * debian 7: `On`
  * ubuntu 12: `On`
  * ubuntu 14: `On`
  * centos 6: `On`

### TraceEnable
* Proposed ansible var: `apache_trace_enable `
* Possible values: `On` | `Off` | `Extended`
* Proposed default value: `Off`
* Distro default values:
  * debian 6: `Off`
  * debian 7: `Off`
  * ubuntu 12: `Off`
  * ubuntu 14: `Off`
  * centos 6: Not set (`On` by default)
I know this is confusing at first glance, but in Ubuntu 14 (Apache 2.4), the security conf moves from `/etc/apache2/conf.d/security` to `/etc/apache2/conf-{available,enabled}/security.conf`. Some filename expansion seemed the easier way around it.