Add the whole gen folder to .gitignore, as well as build.properties

Adding build.properties to .gitignore will force each user to create and
keep its local changes without pushing them to the server.
build.properties is meant to configure each development environment.
Issue #280 - Create build script to automate FieldSurvey app build

*Add build script with target flow-release, which creates the app and
places it in the desired location (default to bin).

*Remove build.properties from the repository to allow independent
development environments for each user.

*Add build.properties.template to ease the creation of the the build
configuration file

*Update README to provide build script execution steps.
Ignore all build.properties files