Renamed "traits" namespace to "trait"

[tonydp03]

Fixes #179. The Alpaka namespace "traits" was renamed to "trait" in all its occurrencies. However, are we sure we want to keep the namespace and not removing it entirely to simplify the code, as @bernhardmgruber suggested?

[psychocoderHPC]

I am against removing the trait namespace. The namespace is separating the free functions the user is touching from the implementations alpaka developers or experts are providing. see https://alpaka-group.github.io/alpaka/namespaces.html

[bernhardmgruber]

I did not check every file, but I think trusting the CI is fine in this case.

[bernhardmgruber]

The commit was made with @tonydp03 as author. @psychocoderHPC do you insist on commiting under the Tools author? And @j-stephan do you want @tonydp03 to update all the copyright headers? I don't care much about both of them.

[psychocoderHPC]

@bernhardmgruber mentioned it please commit your changes with

GIT_AUTHOR_NAME="Tools" GIT_AUTHOR_EMAIL="[email protected]" git commit ...

This PR is mostly processed with search and replace. We try to submit automated changes under an generic user.

[j-stephan]

If we have the tools author I don't think we need to update the copyright header.

[tonydp03]

I'll change the headers, rebase, and squash the new commit with the previous one under the Tools author.