General code improvements

[dobozysaurus]

General improvements for the Config, GoogleDrive2 classes:

• Compatibility for folks running OS X (code referred to several Linux only constructs - /home/* vs /Users/*, drive_linux vs drive_darwin, etc)
• Moved hard-coded URLs for drive_* to configs for easier updating
• Addition of dotenv (https://github.com/cdimascio/java-dotenv) for easier maintenance of environment variables
• Allowed credentials to be read from a file, rather than inserted directly into the environment variables
• Preferred usage of NIO file ops (Files.createDirectories() instead of File.mkdir(), etc) because of the former's preference for failing fast vs boolean returned values that are often unchecked
• Increased usage of Validate.* for better pre-requisite checks
• Import cleanup
• Cleanup of unnecessary diamond types

[dobozysaurus]

Also added: more encapsulation for the Database2 class; made Event and Task first class objects, added unit testing for Database2.

[dobozysaurus]

@matallen @sabre1041 Wasn't sure if you all were looking for contribs on this repo, but figured I'd add some Mac friendly dev functionality and unit testing.

[matallen]

@dobozysaurus Yes, contributions are always welcome, especially broadening the platform in which it runs & can be developed. Please give me some time to look through the changes and I'll get back to you.

[dobozysaurus]

Rebased against master to fix conflicts; added some minor cleanup for ChartsController as well.

[dobozysaurus]

@matallen Given your comments on earlier commits, and its current conflicted state, my thought on this one is to close it and divide it into a series of more focused PRs sans formatting changes.