Added 'getLastAverageVotes' func. to prepare graph data

'getLastAverageVotes' function returns array of 10 average values for 10 last minutes. Every array element is a Javascript object consist of 2 elements:
	{
		"time": time,
		"average": average
	}
If there is less than 10 minutes passed from meeting beginning, rest of array elements will be empty (zero values).
Merge branch 'master' of https://github.com/nsn-wroclaw/innovativeproject-focusmeter