Added bi-directional binding to window show, added openClick window callback

This Pull Request adds two functionalities and provides use case examples. 

**Bi-directional binding of scope.show**
You will now see the marker.showWindow property updated when the user clicks on a map marker to open its infowindow. Previously the property was only updated when clicking on the list.

**openClick callback**
This works in the same way that closeClick does, except its called when the info window is opened. @note it's not called when a user triggers a window to open remotely (ie by clicking on a list of markers). In the provided use case, I close all other open infowindows before opening the requested one. 

Also effectively closes this issue: https://github.com/nlaplante/angular-google-maps/issues/72 although.

**Note**
I changed minimal code, but I noticed a heck of a lot of changes to the dist/*.js files. Are these suppose to be committed with PRs? 

Also, when running `grunt` I got a number of errors from previous commits, FYI. I needed to run `grunt --force` to build, hope this is OK.