update gradle to 5.6
dtbo parser: force use of python 2.7
add android libsparse utils
add sparse image parser: {system|vendor|product}.img
travis: upgrade to bionic(18.04 LTS)
1. make my groovy code more java like
add @groovy.transform.TypeChecked and @groovy.transform.CompileStatic to
eliminate runtime surprise
2. add strict checking before 'pack' task
3. all boot.img.clear* will be hashed and the hash code will be compared to
assert equation
4. upgrade gradle and groovy version
cfig