plink, disabling features, triming the content of parsed urls

- When receiving messages from diaspora, the field "plink" is now filled with the URL of the original post. Previously it contained a link to the own server. Additionally another template variable was defined that contains a link to the own server. That means that an item now can contain these two different links. (a pull request for "vier" with a changed template will follow soon)

- In several networks there is no support for all features of friendica. For example "dislike" is only working with Friendica, in Diaspora you can't like a comment and you can't like a mail or a feed entry. So from now on these features are disabled for the different networks.

- And a small change: Sometimes there were line breaks at the beginning of a parsed description. There is now a "trim" to fix it.