Load the bootstrap stylesheet when using elm-reactor

[n1k0]

The current hack where we inject the stylesheet at runtime is not satisfying; we need to find a way to provide a custom HTML template to elm-reactor, or at least a way to tell the one it generates to use a custom stylesheet.

Reference Elm issue: elm-lang/elm-reactor#138 (some tricks are listed in the comments)

[n1k0]

This may be just solved by using elm-live, which has support for custom HTML file.