Big repository reorganization

The code is divided in three crates:
- plume-common, for the ActivityPub module, and some common utils
- plume-models, for the models and database-related code
- plume, the app itself

This new organization will allow to test it more easily, but also to create other tools that only reuse a little part of
the code (for instance a Wordpress import tool, that would just use the plume-models crate)

plume-common/src/lib.rs

@@ -0,0 +1,28 @@
+#![feature(custom_attribute, iterator_flatten)]
+
+extern crate activitypub;
+#[macro_use]
+extern crate activitystreams_derive;
+extern crate activitystreams_traits;
+extern crate array_tool;
+extern crate base64;
+extern crate chrono;
+extern crate failure;
+#[macro_use]
+extern crate failure_derive;
+extern crate gettextrs;
+extern crate hex;
+extern crate heck;
+#[macro_use]
+extern crate hyper;
+extern crate openssl;
+extern crate pulldown_cmark;
+extern crate reqwest;
+extern crate rocket;
+#[macro_use]
+extern crate serde_derive;
+#[macro_use]
+extern crate serde_json;
+
+pub mod activity_pub;
+pub mod utils;