Implement hotkeys for web UI (#5164)

* Fix #2102 - Implement hotkeys

Hotkeys on status list:

- r to reply
- m to mention author
- f to favourite
- b to boost
- enter to open status
- p to open author's profile
- up or k to move up in the list
- down or j to move down in the list
- 1-9 to focus a status in one of the columns
- n to focus the compose textarea
- alt+n to start a brand new toot
- backspace to navigate back

* Add navigational hotkeys

The key g followed by:

- s: start
- h: home
- n: notifications
- l: local timeline
- t: federated timeline
- f: favourites
- u: own profile
- p: pinned toots
- b: blocked users
- m: muted users

* Add hotkey for focusing search, make escape un-focus compose/search

* Fix focusing notifications column, fix hotkeys in compose textarea

yarn.lock

@@ -1684,6 +1684,14 @@ create-hmac@^1.1.0, create-hmac@^1.1.2, create-hmac@^1.1.4:
     safe-buffer "^5.0.1"
     sha.js "^2.4.8"
 
+create-react-class@^15.5.2:
+  version "15.6.2"
+  resolved "https://registry.yarnpkg.com/create-react-class/-/create-react-class-15.6.2.tgz#cf1ed15f12aad7f14ef5f2dfe05e6c42f91ef02a"
+  dependencies:
+    fbjs "^0.8.9"
+    loose-envify "^1.3.1"
+    object-assign "^4.1.1"
+
 cross-env@^5.0.1:
   version "5.0.5"
   resolved "https://registry.yarnpkg.com/cross-env/-/cross-env-5.0.5.tgz#4383d364d9660873dd185b398af3bfef5efffef3"
@@ -4209,6 +4217,10 @@ mocha@^3.4.1:
     mkdirp "0.5.1"
     supports-color "3.1.2"
 
+mousetrap@^1.5.2:
+  version "1.6.1"
+  resolved "https://registry.yarnpkg.com/mousetrap/-/mousetrap-1.6.1.tgz#2a085f5c751294c75e7e81f6ec2545b29cbf42d9"
+
 ms@2.0.0:
   version "2.0.0"
   resolved "https://registry.yarnpkg.com/ms/-/ms-2.0.0.tgz#5608aeadfc00be6c2901df5f9861788de0d597c8"
@@ -5553,6 +5565,15 @@ react-event-listener@^0.5.0:
     prop-types "^15.5.10"
     warning "^3.0.0"
 
+react-hotkeys@^0.10.0:
+  version "0.10.0"
+  resolved "https://registry.yarnpkg.com/react-hotkeys/-/react-hotkeys-0.10.0.tgz#d1e78bd63f16d6db58d550d33c8eb071f35d94fb"
+  dependencies:
+    create-react-class "^15.5.2"
+    lodash "^4.13.1"
+    mousetrap "^1.5.2"
+    prop-types "^15.5.8"
+
 react-immutable-proptypes@^2.1.0:
   version "2.1.0"
   resolved "https://registry.yarnpkg.com/react-immutable-proptypes/-/react-immutable-proptypes-2.1.0.tgz#023d6f39bb15c97c071e9e60d00d136eac5fa0b4"