Provide block for custom search pages

The way Apache Solr Panels should be used is to create a completely new search page using Page Manager. The /search/apachesolr_search page shouldn't be used, nor should the default /search page. See #1047636: Get rid of confusing search-apachesolr_panels page for an example on how to use the module.

Drupal's search form won't send users to the new search page created in Page Manager. If you're using Panels Everywhere, you may use the "Apache Solr search form" pane on other pages and direct it to your search page's path. But if all you have is blocks, you'll have to form_alter Drupal's search form to do the redirect. I'll see if I can find a good solution for the block system too.

Committing this patch adding a new search block called "Search (Apache Solr Panels)". For now it just lets you enter the path it should redirect to, but I hope to be able to fetch Page Manager pages into a select for users to select from (ideally only ones having a "Apache Solr search results" pane).