nginx config template improvement

As an addition to #1834 config should be more aware of settings in omero.web

This PR propagate it while generating nginx config:

```
bin/omero web config apache
bin/omero web config nginx
bin/omero web config nginx --system
```

In order to test it please set the following in various configurations (that make sense of course) including empty values and check if matching config was generated:

example:
```
bin/omero config set omero.web.static_url '/omero/static/'
bin/omero config set omero.web.force_script_name '/omero'
```
gives:
 - nginx

    ```
    server {
            ...
            location /omero/static {
            ...
            location /omero {
                ...
                fastcgi_split_path_info ^(/omero)(.*)$;
    ```
 - apache
    ```
    ...
    Alias /omero/static /YOUR_OMEROPATH/dist/lib/python/omeroweb/static
    Alias /omero "/YOUR_OMEROPATH/dist/var/omero.fcgi/"

    ```

Please note that static_url and force_script_name are independent
Then they should be documented in the PR description and tested. Do you want to have a go @sbesson? The default `client_max_body_size` is 1MB so uploads > 1MB will fail without this setting:
 * http://nginx.org/en/docs/http/ngx_http_core_module.html#client_max_body_size

Apache buffers client bodies in RAM and does not set a limit by default.

The `send_timeout` setting should probably be synchronized with the changes to `fastcgi_read_timeout` in this PR as well. The default is 60 seconds so you could at your option just remove it. For reference:
 * http://nginx.org/en/docs/http/ngx_http_core_module.html#send_timeout

Was there a particular reason to adjust `client_body_buffer_size` from its default? For reference:
 * http://nginx.org/en/docs/http/ngx_http_core_module.html#client_body_buffer_size