Added supporting of Properties in Group-Interfaces

[programmerr47]

We need to add supporting of val properties in group analytics interface. Thus, the group interface will look like:

interface AnalyticsGroup {
    val single: AnalyticsSingle
}

instead of

interface AnalyticsGroup {
    fun single(): AnalyticsSingle
}

And usage will be like analyticsGroup.single instead of analyticsGroup.single()
Thus, we will eliminate unnecessary brackets

[programmerr47]

As it appeared. Currently val parameters are partly supported for group interface if and only if they have no annotations on properties at all. Need to think how to add support of that...

[programmerr47]

Need to add documentation

[programmerr47]

Added https://github.com/programmerr47/ganalytics/wiki/Interfaces#from-v11