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/opts.py

@@ -18,7 +18,7 @@
 import watcher.api.app
 from watcher.applier import manager_applier
 from watcher.decision_engine import manager
-from watcher.decision_engine.strategy.selector import default \
+from watcher.decision_engine.strategy.selection import default \
     as strategy_selector