Polarion independent templating

[ewuerger]

Work on generic rendering helper methods:

• insert model_element
• insert text_element
• insert heading
• insert table
• insert pagebreak
• link model_element
• ...

for the individual target tool. In this repo we will provide the PolarionTemplateHelper.

[Wuestengecko]

• insert model_element

This sounds very generic, especially with "link model_element" also being a thing. What's this supposed to do?

• insert text_element
• insert heading
• insert table

I'm not familiar with Polarion's specifics, why can't we just use the normal HTML elements for these? Especially table handling sounds like a huge pain to deal with if we need to make a custom function (or, more likely, multiple), instead of just using plain <table>, <tr>, <td> etc. tags.