Add html parsing on Cheerio

[ymkins]

Add htmlSrc option to parse with cheerio for support nested html in translate and translate-attr directives. For example:

<p translate="section.hint">
    <em>Word order</em>
    <a href="https://www.google.com/search?q='word+order+matters'">matters</a>.
</p>
<input type="text" class="form-control" id="mynameId" name="myname"
    translate-attr="{placeholder: 'section.placeholderMyname', title: 'section.titleMyname'}"
    placeholder="Name" title="Edit Name"
    ng-model="vm.myname" ng-required="true"
/>