Clean up BaseDBConfiguration class

Clean up BaseDBConfiguration class

This change isn't too big;  it mainly just attempts to clean up the
BaseDBConfiguration class using best practices.  For example:

* documentation is added surrounding public methods, public constants,
  protected variables, and class headers.
* code logic for parsing "optional" integer properties is abstracted
  into a separate private static function, which returns a default
  value if the given input property cannot be parsed or is not present.
* public functions where the NumberFormatException RuntimeException
  might be thrown have the appriorate "throws" modifier added to their
  function signatures to indicate that the consumer is responsible for
  exception handling.
* constants are extracted in place of "magic numbers"

This is really just code sanitation work.

Change-Id: Ifaf092e10b17f54c7cce0a888aa49bfe8377cdd3
Issue-Id: SDNC-79
Signed-off-by: Ryan Goulding <ryandgoulding@gmail.com>