add method Model\Page::getPlainContent()

[Schlaefer]

Introduces a Model\Page::getPlainContent() which returns the unparsed page content.

The existing Model\Page::getContent() is O.K. for the core but often not very well suited for plugins:

• result is parsed (HTML tags not desired/needed, performance impact)
• triggers parser events (side effects, potential for endless recursion)

I'm not particularly happy with the method name, so if someone has a better idea?

[kicken]

I typically name methods like that with 'raw', as in getRawContent. I think the current name is fine though.

[james2doyle]

+1 for getRawContent()