Wiki rendered syntax simplification part 1: emphasizing markup

Currently, we're using too many class attributes for the generated markup from the wiki syntax, and we're doing this in a bad manner. For example:

• p class="paragraph"
• h2 class="heading-1"
• strong class="strong"
• del class="strike"

The class attribute should only be used with semantics in mind, and saying that all p-s are paragraphs, and all strong-s are strong, this adds no semantics whatsoever, but does increase the size of the transfered files (and the page loading time), the rendering time, the cache size and the size and complexity of the CSS files.

The first part is to solve the emphasizing markup:

- *text* => <strong>text</strong>
- ~~text~~ => <em>text</em>
- --text-- => <del>text</del>
- __text__ => <em class="underline">text</em>