Remove inline CSS

[leonklingele]

Please remove inline CSS as seen here:

1. https://github.com/grevory/bootstrap-file-input/blob/bf93e97d440ca4cb97f7990f4879c187c712128f/bootstrap.file-input.js#L122-127
2. https://github.com/grevory/bootstrap-file-input/blob/master/bootstrap.file-input.js#L131-136

Inline CSS should be turned off in favor of a good CSP.

[leonklingele]

PR: #38