Use sys path mostly from project and move some sys path stuff around.

jedi/evaluate/project.py

@@ -1,7 +1,8 @@
 import os
 import sys
 
-from jedi.evaluate.sys_path import get_venv_path
+from jedi.evaluate.sys_path import get_venv_path, detect_additional_paths
+from jedi.cache import underscore_memoization
 
 
 class Project(object):
@@ -14,11 +15,24 @@ class Project(object):
         if sys_path is None:
             sys_path = sys.path
 
-        sys_path = list(sys_path)
-
+        base_sys_path = list(sys_path)
         try:
-            sys_path.remove('')
+            base_sys_path.remove('')
         except ValueError:
             pass
 
-        self.sys_path = sys_path
+        self._base_sys_path = base_sys_path
+
+    def add_script_path(self, script_path):
+        self._script_path = script_path
+
+    def add_evaluator(self, evaluator):
+        self._evaluator = evaluator
+
+    @property
+    @underscore_memoization
+    def sys_path(self):
+        if self._script_path is None:
+            return self._base_sys_path
+
+        return self._base_sys_path + detect_additional_paths(self._evaluator, self._script_path)