Webstart index template

This fixes customization on webstart template. ```INDEX_TEMPLATE``` has been replaced by ```WEBSTART_TEMPLATE``` to simplify naming convention.

To test it please set the following: 
```
$OMERO_HOME/bin/omero config set omero.web.webstart_template 'webstart/index.html'
```
then open webbrowser and go to ```http://localhost:8000/```
Instead of login page you should see content of the new page. ```WEBSTART_TEMPLATE``` also define custom template within webclient. If you click on the ![icon-omero-insight-toolbar](https://f.cloud.github.com/assets/1065155/2524332/058affc8-b4e0-11e3-8cda-19626b1b7f17.png) you should be able to see the same template.

```WEBSTART_TEMPLATE``` also accept full path, please try also setting:

```
$OMERO_HOME/bin/omero config set omero.web.webstart_template '/YOUR_OMERO_DIR/components/tools/OmeroWeb/omeroweb/webstart/templates/webstart/index.html'
```

WARNING: Please make sure ```omero.web.login_redirect``` is unset