Reorganize datasets and metrics in pathology

[bhashemian]

Description

This PR reorganize pathology-related datasets and metrics into directories similar to main MONAI.

Status

Ready

Types of changes

• Non-breaking change (fix or new feature that would not break existing functionality).
• Breaking change (fix or new feature that would cause existing functionality to change).
• Integration tests passed locally by running ./runtests.sh -f -u --net --coverage.
• Quick tests passed locally by running ./runtests.sh --quick --unittests.

[madil90]

/build

[wyli]

thanks, this is mostly non-breaking, looks good to me -- please confirm @Nic-Ma

[bhashemian]

thanks, this is mostly non-breaking, looks good to me -- please confirm @Nic-Ma

Thanks, @wyli! That's correct, they are essentially non-breaking changes but they just affect the way to import them.