cucumber test for identity creation

Add a cucumber test for identity creation scenario.

end2end-tests/cucumber-features/identity_creation.feature

+Feature: Identity creation
+
+  Scenario: alice invites a new member to join the web of trust
+    # 6 ĞD covers:
+    # - account creation fees (3 ĞD) 
+    # - existential deposit (2 ĞD)
+    # - transaction fees (below 1 ĞD)
+    When alice sends 6 ĞD to ferdie
+    # alice last certification is counted from block zero
+    # then next cert can be done after cert_period
+    When 15 block later
+    When alice creates identity for ferdie
+    Then ferdie identity should be created
+    When ferdie confirms his identity with pseudo "Ferdie"
+    Then ferdie identity should be confirmed