Generate static HTML for stream blocks, with the common structure shared with ListBlock moved into a parent 'structure' template
remove macro.js (folding that code into the 'sequence' code shared by list and stream will make more sense)
establish a common pattern of specifying dependencies of block factories, so we don't have to repeat the code for iterating over them for media and html_declarations
apply javascript initializers to children of StreamBlock
consistently rename js_declaration to js_initializer