Added BackgroundExecutor and BackgroundTask
BackgroundExecutor hooked to Controller
Test for BackgroundExecutor
Demo to show that UI doesn't freeze while a background task is processed
AsyncExecutor use the number of cores minus 1
Added semaphore to control completePercentage lock
Added finally clause to ensure background tasks are removed from the list
Javadoc clarifying that task results listeners are invoked from UI thread
Added BackgroundExecutor as done parameter
Merge pull request #268 from anserran/background-executor

Background Executor to execute long running tasks
Change output type to json
Delete duplicated json files: they were move to build-tools but not delete from engine/schema
Merge pull request #270 from anserran/json-outputtype

Change output type to json
Updated viewport
Updating travis CI configuration to use android-19 API. Resolve build problems in #274
Merge pull request #271 from angeldelblanco/delete-duplicate-json

Delete duplicated json files:
Merge pull request #275 from imartinezortiz/travis-android-fix

Updating travis CI configuration to solve build problems in #274
Updating travis-ci config to use android SDK symbolic names instead of numeric id
Merge pull request #283 from imartinezortiz/travis-android-fix

Updating travis-ci config to use android SDK symbolic names
Configure maven-deploy version at root POM level