Added simple Python install check

Now tries to run the "python" command first, if it fails it tries default install path "C:\python27\python.exe".
Returns "Check Python install" if those 2 fail.

Extract keys.bat

@@ -2,10 +2,10 @@
 python walletaid.py
 IF ERRORLEVEL 1 (
 	CLS
-	"C:\python27\python.ee" walletaid.py
+	"C:\python27\python.exe" walletaid.py
 )
 if ERRORLEVEL 1 (
 	CLS
 	ECHO Check Python install
 )
-@pause
+@pause