* [NOD-423] Rename BestBlock to SelectedTip
* [NOD-423] Implement GetSelectedTip RPC command
* [NOD-423] Add help to getSelectedTip command
* [NOD-423] Fix getSelectedTip test
* [NOD-423] Fix tests so they would compile. These tests will need to be rewriten at some point.
* [NOD-423] Make integration test compile. Test need to be revisited
* [NOD-423] Rename variables
* [NOD-423] Change comment s about best block to selected tip.
* [NOD-423] Update comment
* [NOD-423] Change height to bluescore
