ATK mappings for ins and del need to be updated

[joanmarie]

#141 added mappings for ATK, however there are a couple of issues:

1. There is no attribute included to identify that the ATK_ROLE_SECTION is an insertion or deletion. In order to be consistent with what has been done for other elements which have corresponding ARIA roles, I propose adding xml-roles:insertion for ins and xml-roles:deletion for del. This will be going into the Core-AAM.
2. As agreed upon earlier, we should wait for the platform new roles to land in ATK and AT-SPI2. That has happened. See https://gitlab.gnome.org/GNOME/atk/commit/e3856ee2. The Core-AAM will also contain the new roles (ATK_ROLE_CONTENT_INSERTION and ATK_ROLE_CONTENT_DELETION)

I'm happy to do a pull request, but I don't know how you feel about when it's best to do 2.

[joanmarie]

Went ahead and did the pull request just in case. If you disagree, we can close it.

[scottaohara]

Hey @joanmarie. 2 prs are fine with me. The second can be noted as not ready for merge until the time is right.