improve less resource handling
change exception type and minor improvements to samples ui
change debug log messages and update to less4j 0.0.9
Issue #131 Minor improvement of javadoc
Issue #131 AbstractCompiledResource should not cache InputStream because once consumed it will return an empty result from there on.

LessResourceStreamLocator cache fields should not be 'static' because this may lead to problems when wicket-bootstrap.jar is put in shared lib folder of the web container.
IResourceStreamLocator is a singleton in an Wicket application so there are still just one instance of those fields.
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Merge pull request #131 from l0rdn1kk0n/less

improve less resource handling