Data tests

DoubleData:

• Cleaned out deprecated methods
• Added missing tests

Indexing:

• Cleanup and added missing tests

Interpolater:

• Fixed incorrect descriptions
• Added tests for edge cases not covered

Interval* classes:

• Consistency across 1, 2, and 3D Interval* classes
• Added tests and cleaned/corrected javadoc

Resolves #44 (closed)