better template inheritance

[jeremybmerrill]

Create a method for a search engine to use, for instance, the blob template for each template, but a custom one, say, my_search for the search_form. (Right now, you'd have to create a custom search_form/my_search.template, query_builder/my_search.js, detail_view/my_search.template, and list_view/my_search.template even if you only wanted to customize one.)

[jeremybmerrill]

we should also allow setting template names by page type

'jeb-bush-emails': {
       list_view: 'email',
       detail_view: 'email',
       search_view: 'jeb-email',
       query_builder: 'jeb-email'
     }

if you wanted only one or two templates to be special and use existing ones for others.

now that this is set thru google spreadsheets, solving it will be a little different, maybe a third Spreadsheet sheet that overrides the data_type column in the first sheet (and that joins on index_name like the sample searches one does).