client.state implementation for bf3 parser

This commits implements the Client.state behavior for Bf3 parser.  

- override Client.state with dynamic property
- add ´isAlive´ to the Client class

```python
if client.isAlive():
    # happy birthday
    ...

if client.state == b3.STATE_ALIVE:
    # happy birthday
    ...
elif client.state == b3.STATE_DEAD:
    # :(
    ...
```