Add Mastodon frontend.

lib/pleroma/plugs/oauth_plug.ex

lib/pleroma/web/endpoint.ex

lib/pleroma/web/mastodon_api/mastodon_api_controller.ex

lib/pleroma/web/mastodon_api/views/mastodon_view.ex

lib/pleroma/web/router.ex

...leroma/web/templates/mastodon_api/mastodon/index.html.eex

...leroma/web/templates/mastodon_api/mastodon/login.html.eex

...ks/Montserrat-Medium-5f797490f806b3b229299f0a66de89c9.ttf

...Montserrat-Regular-080422d4c1328f3407818d25c86cce51.woff2

...s/Montserrat-Regular-6a18f75e59e23e7f23b8a4ef70d748cd.ttf

.../Montserrat-Regular-b0322f2faed575161a052b5af953251a.woff

priv/static/packs/about-d6275c885cd0e28a1186.js

priv/static/packs/admin-1bab981afc4fd0d71402.js

priv/static/packs/appcache/manifest.appcache

priv/static/packs/appcache/manifest.html

priv/static/packs/application.js

priv/static/packs/base_polyfills-0e7cb02d7748745874eb.js

priv/static/packs/common.css

priv/static/packs/common.js

priv/static/packs/default-99ffdcf166b2dedef105.js