wip inset block helper

currently only works in isolation
make methods private
add dough renderer
dough render deals with rendering
fix test
remove dough renderer.

inset block now has own renderer for now
remove unused option
load dough rails helpers by default
inset block partial path is namespaced to dough

this mean users can have their own implementation
simply add a view at dough/helpers/inset_block/inset_block
to override the default behaviour
it just needs to be earlier in the view paths
add inset block to spec dummy docs
Merge pull request #93 from moneyadviceservice/inset-block-helper

Inset Block Rails Helper