Add empty query norm. test.
Add empty frag/query norm. test.
Add %20 in key id for SQLite driver tests.

* Provides better coverage.
Generalizing driver unit tests.

* Add super-class (boilerplate) common to all driver
  JUnit test classes.
Generalizing file-based driver unit tests.

* Add super-class (boilerplate) common to all JUnit test
  classes for testing drivers that use the local file-system.
Add utility for checking failed loads.
Migrate K2FileSystemDriverTest to new framework.

* Improves code-reuse in testing drivers.
* More concise/readable tests.
Migrate SqliteDriverTest to new framework.
Add K2-native in-memory key storage driver.

* For temporary storage of keys (until the
  the K2Context is garbage collected).
* Unit tests included.