Change distance evaluation period from Sessions to Blocks

Closes #202 (closed) Closes #207 (closed)

• Create evaluation period in block.
• Update tests.
• Weight accounting
• Upgrade the distance oracle.
• Fix #207 (closed).
• Closes #174 (closed): the worst and simplest estimation equates to one evaluation being 0.0037% of a block's weight, based on the current reference machine. To maintain a reasonable load on the system, it's advisable that the cumulative weight of all evaluations does not surpass 5-10% of a block's capacity. Consequently, setting MAX_EVALUATIONS_PER_SESSION between 1 300 and 2 600 would ensure safe operation.

end2end-tests/cucumber-features/identity_creation.feature

@@ -24,9 +24,9 @@ Feature: Identity creation
     Then dave should be certified by bob
     Then dave should be certified by charlie
     When dave requests distance evaluation
-    Then dave should have distance result in 2 sessions
-    When 30 blocks later
-    Then dave should have distance result in 1 session
+    Then dave should have distance result in 2 periods
+    When 14 blocks later
+    Then dave should have distance result in 1 period
     When alice runs distance oracle
-    When 30 blocks later
+    When 7 blocks later
     Then dave identity should be member