Update perf recipe
Update perf recipe

Changes made:

- Adding the bundle link tag in the page to improve initial load
- Presenting both the initial link tag approach and the `loadElements` approach as separate
- Parameterizing `loadElements` with a path to the bundle and a callback
- Using in-page markup for the splash example instead of innerHTML to improve first paint

@ebidel @samsaccone PTAL

lordoftheflies/mlm-portal,stephenzsy/charon-frontend,SB-Technology-Holdings-International/WateringWebClient,SB-Technology-Holdings-International/Water,alexpaluzzi/polymer-starter-kit,stefanoantonel/brainpower,Sykkro/penny-web,StartPolymer/polymer-starter-kit-plus,gertcuykens/polymer-starter-kit,felixzapata/polymer-starter-kit,abdonrd/polymer-starter-kit,SB-Technology-Holdings-International/WateringWebClient,alexpaluzzi/polymer-starter-kit,RoyKoh/Project-3,gertcuykens/polymer-starter-kit,Serious-Rage/poligomy,StartPolymer/polymer-starter-kit,flaiker/polymer-starter-kit,semafloor/semafloor-test-alpha,SB-Technology-Holdings-International/WateringWebClient,felixzapata/polymer-starter-kit,michaetto/f16,plusCubed/pluscubed-site,michaetto/f16,Serious-Rage/poligomy,gick/reveries-project,semafloor/semafloor-test-alpha,stefanoantonel/brainpower,RoyKoh/Project-3,Ex-ante-Labs/shopper.ninja,Serious-Rage/poligomy,klarkc/polymer-loopback-starter-kit,mtusk/polymer-starter-kit,markovuksanovic/polymer-starter-kit,Ex-ante-Labs/pivot-ahead,Ex-ante-Labs/pivot-ahead,anthonybrown/polymer-starter-kit,klarkc/polymer-loopback-starter-kit,markovuksanovic/polymer-starter-kit,JnJSW/dttdata,SB-Technology-Holdings-International/Water,klarkc/polymer-loopback-starter-kit,StartPolymer/polymer-starter-kit-plus,anthonybrown/polymer-starter-kit,lordoftheflies/mlm-portal,lordoftheflies/mlm-portal,trendystore/store,andrefuller/PolymerTrailerViewer,Sykkro/penny-web,SB-Technology-Holdings-International/Water,Sykkro/penny-web,flaiker/polymer-starter-kit,gick/reveries-project,FaellCarvalho/Geo-Location,plusCubed/pluscubed-site,FaellCarvalho/Geo-Location,JnJSW/dttdata,gick/reveries-project,mtusk/polymer-starter-kit,andrefuller/PolymerTrailerViewer,RoyKoh/Project-3,grebett/polymer-starter-kit,michaetto/f16,semafloor/semafloor-test-alpha,SB-Technology-Holdings-International/WateringWebClient,gick/mobile-polymer-starter-2,markovuksanovic/polymer-starter-kit,stephenzsy/charon-frontend,stephenzsy/charon-frontend,felixzapata/polymer-starter-kit,FaellCarvalho/Geo-Location,trendystore/store,abdonrd/polymer-starter-kit,SB-Technology-Holdings-International/Water,StartPolymer/polymer-starter-kit,trendystore/store,grebett/polymer-starter-kit,grebett/polymer-starter-kit,gick/mobile-polymer-starter-2,gertcuykens/polymer-starter-kit,andrefuller/PolymerTrailerViewer,SB-Technology-Holdings-International/Water,JnJSW/dttdata,alexpaluzzi/polymer-starter-kit,gick/mobile-polymer-starter-2,Ex-ante-Labs/shopper.ninja