Make osf addon modules Common-JS compatible

Purpose
------------
Addresses the following checklist items in CenterForOpenScience/osf/pull/1215: 

- [x] Make all addons' modules CommonJS-compatible and add initialization modules (deprecates static asset configuration in addons' __init__.py files)
    - [x] dataverse
    - [x] figshare
    - [x] s3
    - [x] osfstorage
    - [x] github
    - [x] forward  

Changes
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Follows the proposed solution outlined in CenterForOpenScience/osf/pull/1215:
- Require imports and export modules using `module.exports = Foo`
- Initialize js modules in separate config files instead of in script tags