Change license to Apache-2.0 with LLVM exceptions

[matthiasdiener]

(per our email discussion)

Same could be done for charm4py, projections, ...

[PhilMiller]

Not that you need my approval, but I'm glad to see this finally come out!

[matthiasdiener]

Next step:

add a NOTICE file (similar to https://github.com/spack/spack/blob/develop/NOTICE) with the following information:

• acknowledging UIUC, and Charmworks, and multiple grants (not individually listed) from NSF, NIH, DoE that directly or indirectly supported this work.

[lvkale]

When we change this, we should also change the license in the readthedocs (or remove it from there)
https://charm.readthedocs.io/en/latest/license.html

[ericjbohm]

Changed to target Charm-8.0.0, which will just be Charm-7.0.0 with the license and related doc changes.

[matthiasdiener]

When we change this, we should also change the license in the readthedocs (or remove it from there) https://charm.readthedocs.io/en/latest/license.html

That license is just #included from the main LICENSE file, so a change there will automatically be reflected on readthedocs.

[ericjbohm]

Next step:

add a NOTICE file (similar to https://github.com/spack/spack/blob/develop/NOTICE) with the following information:

• acknowledging UIUC, and Charmworks, and multiple grants (not individually listed) from NSF, NIH, DoE that directly or indirectly supported this work.

Draft of NOTICE file added to this PR.