Code Formatting with EditorConfig

[anthonysena]

Some time ago, code formatting was discussed on the OHDSI forums here:

http://forums.ohdsi.org/t/indent-rules-at-least-for-js-at-least-for-atlas/1783/8

The decision that was made based on a vote was to use tabs for indenting. @cerdman (
hoping I'm tagging the right person) proposed using http://editorconfig.org/ to enforce code formatting standards since it is a single file that is included in the repository and is compatible with many different IDEs.

From the architecture discussion today, we decided that this would be worthwhile to do after tackling #633 and putting it here so we don't lose track of it (again).