small inconsistency in javascript tracking API + documentation updates

[matt]

As documented in:  http://forum.piwik.org/index.php?showtopic=1079

we would like to:

• resolve inconsistency; probably all setX should "replace" the list of classes, except the piwik_* default css class should always be in the list.
• update the documentation to make it a bit more clear

Thanks!

[vipsoft]

Should we rename the functions for consistency too?

[matt]

yes it sounds like a good idea. what do you think about:

• all functions accept either array or string names, or a simple string
• all function named setBlahClasses()
• we keep the old functions as briges and call the new ones - for backward compatbility for 0.4 users that already use the API

[vipsoft]

(In [1309]) refs #816 - added setDownloadClasses() and setLinkClasses() for consistency with setIgnoreClasses(), refactoring, and additional tests

[vipsoft]

To do: update http://piwik.org/docs/javascript-tracking/

[matt]

updated doc in http://piwik.org/docs/javascript-tracking/

thanks vipsoft