Allow DI for axios instance

[jeffturcotte]

For VuexModule.

In some cases, axios may need to be configured to send certain headers or something similar to the server. Ideally, an axios instance could be provided to overload the default one.

[khamer]

There's work for this in the 0.9.2 tag, but the 0.9.2 tag ran into other issues I was unable to resolve and I removed it from NPM until I can fix those issues.