Graceful exit when no states to run (#815)

* rm unnecessary return, change assert to graceful handle

* Add regression test

* Add regression test

* Correct logic

* Rm unnecessary check

This branch is unnecessary, if this condition is true, then ultimately
the executor will do nothing, and we'll simply return anyway.

* Raise NoAliveStates if no alive states to execute

* docstr update

* Update mult_tx_analysis to handle NoAliveStates

* Fancy

* Update test

* Codeclimate fmt

* fmt

* better readability

* add docstr

tests/binaries/795.sol

@@ -0,0 +1,7 @@
+contract Simple {
+    function f(uint a) payable public {
+        if (a == 65) {
+            revert();
+        }
+    }
+}