Sqlite as storage backend (#1)

Some platforms has some problems with file locking, so I was forced to use an alternative. SQLite seems be the best option currently available


* Migrated to an sqlite database

* Removed unnecessary IOExceptions

* Removed an util class not needed anymore

* Updated README.md and docker-compose.yml to reflect new storage mechanism

build.gradle

@@ -24,6 +24,8 @@ jar {
 dependencies {
 	compile "com.sparkjava:spark-core:2.8.0"
     compile 'com.qmetric:spark-authentication:1.4'
+    compile group: 'org.xerial', name: 'sqlite-jdbc', version: '3.30.1'
+
 }
 
 application {