* component build support for both python2 and python3
* add sample test
* remove the annotations for python2 component build
* add pathlib for python2 component build
* fix component build unit test
* fix bug in the dockerfile generator
* remove exist_ok in path.mkdir to make python2 compatible
* adjust unit test
* remove pathlib dependency for python2 component build
* remove the pathlib codes in python3 component build, but use python2 code instead; add a todo to create a new sample
* add requirement to component image build
* add unit test for DependencyVersion
* add unit tests, fix bugs
* revert some unit test change
* include the package name inside the VersionedDependency, enable the unit test for the component builder
* disable the component image build, this is done in another PR
* update the version name to dependency
* delete unuseful tests and add more useful unit tests
* add unit tests
* fix some unit tests
* fix bug in DependencyHelper