Add Gradle build file with wrapper configuration
Generate Gradle wrapper artifacts

See http://www.gradle.org/docs/current/userguide/gradle_wrapper.html
Configure Gradle build

 - Set version at 0.1.0-SNAPSHOT, per http://semver.org practices
 - Configure dependencies per existing Maven pom
 - Resolve dependencies from jcenter by default, mavenLocal for custom
   BitcoinJ and TomP2P binaries (which still must be built separately)
 - Copy non-java files (fxml, etc) from src/main/java when processing
   resources

`./gradle build` is now completes successfully.
Configure Gradle application plugin

 - `./gradlew run` to launch Bitsquare
 - `./gradlew installApp` to create scripts in build/install/bitsquare

See http://www.gradle.org/docs/current/userguide/userguide_single.html#application_plugin
Add Gradle OneJar plugin

For creation of a self-contained executable jar.

Run:
 - `./gradle executableJar`
 - `java -jar ./build/libs/bitsquare.jar

Note that actually executing the jar fails with an exception from
io.bitsquare.util.AppDirectoryUtil.createDirIfNotExists. This will be
fixed later. The purpose of this commit is only to establish the
executable jar infrastructure.
Remove Maven pom
Merge branch 'gradle'