Stemmers supported in Solr 3.x and updated stopwords

I already committed the stopwords and created a new patch that only contains the logic.
I applied these modifications to the code:

• Display the minimum required solr version for a stemmer in the selection form.
• Removed fallback to Porter Stemmer because it will create Illegal configurations. Display an error instead.

Beside some more testing, these additional TODOs need to be implemented within function apachesolr_multilingual_get_stemming_filters():

• Distinguish between solr versions. Not all filters of a chain are available in each solr version. See https://wiki.apache.org/solr/MultitermQueryAnalysis
• Do we need to disable LowerCaseFilterFactory if the filters contain a language specific lower case filter factory?

The logic removed the protected words from the default snowball stemmer. Here's a updated patch.

I already committed the patches to git. But the TODOs of #3 are still open and require additional work.