Fix Incorrect Usage of Rank/Task/etc. in Datatypes Chapter

[wesbland]

Problem

Replace the incorrect usage of the words "rank", "task", etc. to be correctly specified and reflective of the underlying group, communicator, file, or window.

Proposal

Read through the entire chapter to find all problematic instances and correct them.

Changes to the Text

There is unlikely to be a one-size-fits-all solution so the chapter committee will need to consider each occurrence.

Impact on Implementations

None

Impact on Users

We will hopefully begin the process of avoiding the incorrect terminology of referring to processes as ranks and other incorrect usages.

References and Pull Requests

There was a catch-all issue to correct this in #455, but this is being divided up to cover all chapters.

[bosilca]

Nothing to be done for the datatype chapter.