Gradle improvements

Add gradle wrapper
Specify gradle 1.7 for building.
Updated .gitignore file
Remove unused project.properties file
Update jsch library
Define relay-example as a runnable application
Update gradle wrapper to 1.8

Also update the android gradle plugin
Resolve NPE

NPE if changing preferences while not connected.
Show fingerprint instead of serialnumber

When connecting using ssl, show the key fingerprint instead of the
serialnumber.

Fixes #84.