enforce structure of html for definitions and theorems

[cuppajoeman]

Every theorem should have this form

<div class="theorem" id="theorem-...">
    <div class="title">...</div>
    <div class="content">...</div>
    <div class="proof">...</div>
</div>

Therefore the user creating the html still is able to see the structure of general theorem without having to care too much about how it will be styled.

If a user creates a theorem and it doesn't contain the required parameters a warning should be shown on the theorem.

We can construct the styles by using template files and then injecting the content they wrote between the correct divs