MDL-80246 tiny_equation: Escape elementid in the data-target attribute

Tabs use the value of the data-target attribute of the active tab link
to find and display the appropriate tab content. In some situations the
elementid value that is used to generate the data-target may contain
certain characters that have a special meaning in the selector context
(e.g. ".", ",", "#") and because of that the target element cannot be
correctly identified. To fix this problem the elementid value needs to
be escaped prior to generating the data-target attribute.