Begin moving web server to a separate crate. (#448) r=bgrins

This doesn't yet introduce a working Cargo.toml for 'mentatweb', but it
does allow RLS to build correctly without errors, and it reduces the
core library's dependency space, which is more important in the short
term.

Cargo.toml

@@ -18,9 +18,7 @@ rustc_version = "0.1.7"
 
 [dependencies]
 chrono = "0.3"
-clap = "2.23"
 error-chain = "0.8.1"
-nickel = "0.9.0"
 time = "0.1"
 
 [dependencies.rusqlite]

tools/mentatweb/src/main.rs

@@ -9,17 +9,19 @@
 // specific language governing permissions and limitations under the License.
 
 extern crate clap;
-#[macro_use] extern crate nickel;
 
-use nickel::{Nickel, HttpRouter};
+#[macro_use]
+extern crate nickel;
 
 extern crate mentat;
 
-use clap::{App, Arg, SubCommand, AppSettings};
-
 use std::u16;
 use std::str::FromStr;
 
+use clap::{App, Arg, SubCommand, AppSettings};
+
+use nickel::{Nickel, HttpRouter};
+
 fn main() {
     let app = App::new("Mentat").setting(AppSettings::ArgRequiredElseHelp);
     let matches = app.subcommand(SubCommand::with_name("serve")