Add field aliases and further clean-up the base query class.

Per dww and DamZ - for advanced uses of Apache Solr (such as project_solr) we should allow a mapping of field names that show up in the url to more meaningful names.

for example:

'smfield_project_release_api_terms' -> 'drupal_core'

So our search URL would look something like:

/search?q=Views&filters=drupal_core:6.x

instead of:

/search?q=Views&filters=smfield_project_release_api_terms:6.x

In order to accomplish this we probably need a little more cleanup in query class, at least, and perhaps some additional abstraction in the modules.