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.
You might be able to take advantage of some simplified Scala syntax here for multi-line strings:

 ```scala
val theWarning="""  // CR/LF
first line
second line
/* ... */
last line"""
```