add ktlint plugin to project and apply default code style (#2209)

* add ktlint plugin to project and apply default code style

* some manual adjustments, fix wildcard imports

* update CONTRIBUTING.md

* fix formatting

app/src/main/java/com/keylesspalace/tusky/di/Injectable.kt

@@ -13,11 +13,10 @@
  * You should have received a copy of the GNU General Public License along with Tusky; if not,
  * see <http://www.gnu.org/licenses>. */
 
-
 package com.keylesspalace.tusky.di
 
 /**
  * Created by charlag on 3/24/18.
  */
 
-interface Injectable
+interface Injectable