[DO NOT MERGE] Mount PensionsCalculator (behind a feature flag)

* introduces bowndler for bower/bundler integration
* references pensions_calculator branch on github until pensions_calculator released gem is ready to be mounted

This PR should only be merged once the pensions_calculator is hooked in from a built gem.
Throws an error when this is attempted.

```
ExecJS::ProgramError Exception: Unexpected token name «pensionsCalculator», expected punc «,» (line: 55, col: 4, pos: 1291)

Error
    at new JS_Parse_Error (/private/tmp/user-jgilbraith/execjs20140730-97896-xutau4.js:2357:10754)
    at js_error (/private/tmp/user-jgilbraith/execjs20140730-97896-xutau4.js:2357:10973)
    at croak (/private/tmp/user-jgilbraith/execjs20140730-97896-xutau4.js:2357:19198)
    at token_error (/private/tmp/user-jgilbraith/execjs20140730-97896-xutau4.js:2357:19335)
    at expect_token (/private/tmp/user-jgilbraith/execjs20140730-97896-xutau4.js:2357:19558)
    at expect (/private/tmp/user-jgilbraith/execjs20140730-97896-xutau4.js:2357:19696)
    at /private/tmp/user-jgilbraith/execjs20140730-97896-xutau4.js:2357:28190
    at /private/tmp/user-jgilbraith/execjs20140730-97896-xutau4.js:2357:20069
    at expr_atom (/private/tmp/user-jgilbraith/execjs20140730-97896-xutau4.js:2357:27358)
    at maybe_unary (/private/tmp/user-jgilbraith/execjs20140730-97896-xutau4.js:2357:30108)
nil
```