jshint fixes

This pr cleans up a lot of jshint issues and focus on syntax issues only. I have not changed the behavior of the source code.

Within the `contribution.md` we mention:

* Unless required __no semicolons__ they are not required
* Short one-line `if` statements do not require nipple brackets (provided functionality is clear)

I changed those, because within a core xmpp lib we should not focus on beauty of code but on stability. Therefore I propose to change this. In case you do not agree we need to change the `.jshintrc` to meet our coding standard.

For the time being I excluded the `examples` from jshint test.