Tidy up - Watcher Decision Engine package

Some Python class and packages need to be renamed
for a better compliance with the shared terminology
which provides a better understanding of Watcher
objects and components by every contributor.

This patchset is there to change the code structure by adding the folder
"strategies" and "loading".

Partially implements: blueprint glossary-related-refactoring

Change-Id: I56fb24ee6762b3186eccde5983233e17bb227cc1

watcher/api/app.py

@@ -22,7 +22,7 @@ import pecan
 from watcher.api import acl
 from watcher.api import config as api_config
 from watcher.api import middleware
-from watcher.decision_engine.strategy.selector import default \
+from watcher.decision_engine.strategy.selection import default \
     as strategy_selector
 
 # Register options for the service