[CS-4905] added possibility to change user image resolution

Related to ticket: http://dev.sourcefabric.org/browse/CS-4905

There is added possibility to read user data and read logged in user data using Omnibox.

**Omnibox URL:** http://example.com/omnibox/login/?format=json

**Supported parameters in Ajax call:**
 - **imageWidth** - user image width (e.g. 50)
 - **imageHeight** - user image height (e.g. 50)
 - **imageSpecification** - user image specification ('crop' or 'fit')

if not above parameters defined, default options will applay:
- width: 80
- height: 80
- specification: fit


**User data in response:**
- realName
- username
- avatar

**Example response:**
```
{"helpUrl":"http:\/\/www.sourcefabric.org\/en\/products\/newscoop_support\/","locale":"en","userData":{"realName":"Amerigo Vespucci","username":"amerigo","avatar":"\/images\/cache\/50x50\/crop\/images%7Cdc1989572b1a6a68f1981597d0a79eadd2df98df.jpg"},"response":"OK"}
```