improvements to data resolution

[dbarrosop]

fixes #621

When resolving data nornir would start climbing up the tree until reach the defaults, however, the desired behaviour was to climb the tree and then back down for the next group before checking reaching the defaults, which should be checked only as a last resort.

For instance, with the tree below:

         host
     g1       g2
  g11 g12
        defaults

Before the behaviour was host -> g1 -> g11 -> defaults and now it is host -> g1 -> g11 -> g12 -> g2 -> defaults

In addition, this introduces two new methods:

1. extended_data, which returns the data of a given host or group, including its inherited data
2. extended_groups, which includes a list of groups the host or group belongs to including its inherited groups

Finally, the dict method was resolving the attributes of the hosts and groups, which wasn't supposed to happen, it's been fixed

[dbarrosop]

@no-such-anthony would you mind taking a look? And thanks for the pointers/comments

[no-such-anthony]

@dbarrosop Perfect, and the scenarios I had are all returning the correct inherited values.