updating rewrite rules configurator

This should fix the issue reported on the forum where rewrite rules were hardcoded. Now it should create the rule if ```FORCE_SCRIPT_NAME``` is set.

1. 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:

```
$OMERO_HOME/bin/omero config set omero.web.force_script_name '/omero/'
$OMERO_HOME/bin/omero config set omero.web.force_script_name '/omero'
```
You should see in both cases
```
RewriteEngine on
RewriteRule ^/?$ /omero/ [R]
```

2. Then set ```FORCE_SCRIPT_NAME``` to:
```
$OMERO_HOME/bin/omero config set omero.web.force_script_name
```
and check if RewriteRules disappeared