Allow path-like strings to specify nested properties

[rummelsworth]

Attempting to resolve #1385 by using _.get in ModelKey.scopeOrModelVal.

Verified to work against MCVE at #1385, and our main example template seems to run with all functionality and with no console errors.

Unless _.get is already used elsewhere in the source, this introduces a dependency on lodash 3.7.0+.

[cthrax]

👍 LGTM

[rummelsworth]

Thanks.

[QuentinFchx]

This commit broke our code.
Our code looks like this:

<ui-gmap-markers models="models" coords="'location'" click="'onClick'">
    <ui-gmap-windows show="show">
        <div ng-non-bindable></div>
    </ui-gmap-windows>
</ui-gmap-markers>

$scope.models = [
{onClick: ()=>{}}
]

Since this commit, this line breaks because click is a string.

EDIT: My bad, this is not due to this commit (I did a quick blame but this is cleary not the cause).
I will dig further and keep you posted. It works in the 2.0 branch.