Support multiple calendar configs

[glennjacobs]

While using this plugin to create a resource timeline, I noticed that all the configuration is at the plugin level. So it seems that if I wanted two instances of a calendar with different configs, it's essentially impossible currently.

Maybe it would be good if the config could also be set at the widget level?

[sitenzo]

@glennjacobs
I was just reading this because i looked for something just like this.
Did not see any Pull request so i made one #130

@saade
Can you check my code and if you are happy merge it?