GEOMESA-144 Set temporal index variable by default if not selected by user

GEOMESA-144,GEOMESA-140
    
    GEOMESA-140 Warn users about missing temporal component of index
    This commit adds a warning when a user neglects to properly set SF_PROPERTY_START_TIME in the UserData. Such a mistake is non-fatal, but does impact performance.
    
    GEOMESA-144 Set temporal index variable by default if not selected by user
    This commit will set SF_PROPERTY_START_TIME for the user if only one time attribute is present in the SimpleFeatureType, and emit a notification to this effect.
I'm for a single space after :'s and ,'s.  
As a subtle note, :'s can be in class names.  
The first link points out that 
```
value :::
``` 
is valid Scala.
http://docs.scala-lang.org/style/types.html#annotations
http://code.bizo.com/scala-style-guide/white-space.html