updating rewrite rules configurator

This should fix the issue reported on the forum where ```RewriteRules``` were hardcoded. Now it should create the rule if ```FORCE_SCRIPT_NAME``` is set.

- To test follow web deployment on apache http://www.openmicroscopy.org/site/support/omero5.1-staging/sysadmins/unix/install-web.html. Check if setting ```FORCE_SCRIPT_NAME``` to the following gives you the same ```RewriteRules```:

```
$ bin/omero config set omero.web.force_script_name '/omero/'
$ bin/omero config set omero.web.force_script_name '/omero'
```
You should see in both cases
```
RewriteEngine on
RewriteRule ^/?$ /omero/ [R]
```
Start apache and access web on ```http://localhost/omero/```

- Then set ```FORCE_SCRIPT_NAME``` to:
```
$ bin/omero config set omero.web.force_script_name
$ bin/omero config set omero.web.static_url '/static/'
```
and check if ```RewriteRules``` disappeared. Update apache config, restart apache and access web on ```http://localhost/```

cc: @manics