Feature - Support for user-defined configuration files

[hhandoko]

Outcome Desired

User should be able to supply application configuration via a configuration file as opposed to passing a number of system properties (e.g -Dcassandra.migration.scripts.location=...).

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Definition of Done

• Use Typesafe Config library to load configuration data [1]
• Refactor methods to read from configuration object than reading system properties directly.

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Out of Scope

• N/A

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How to Demo

• Use external configuration file to run integration test.
• Use system variable to override external configuration file values in integration test.

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Notes:
[1] - https://github.com/typesafehub/config

[hhandoko]

Implemented in #51 .