Implement memcached caching of DAS sources to speed up DAS wizard
Implement memcached caching of DAS sources to speed up DAS wizard

Also changed filtering implementation to allow it to work with caching
and to work on more than just name in wizard
- from branch

Ensembl/ensembl-webcode,Ensembl/ensembl-webcode,Ensembl/ensembl-webcode,Ensembl/ensembl-webcode,Ensembl/ensembl-webcode