Remove all references to Mandel

[arhag]

Remove all references to Mandel or mandel from within the antelope-3.0 branch of cdt. The submodule repos referenced from the antelope-3.0 branch should not need any changes. There are mentions of mandel in cdt-llvm which are in reference to Mandelbrot and not the Mandel used in the context of EOSIO; these should not be touched.

Also, update the URLs referencing eosnetworkfoundation org repos to use the corresponding ones in the AntelopeIO organization.

After AntelopeIO/leap#1 has been completed, ensure that you can still build CDT with integration tests (has dependency on Leap/EOSIO). In addition, ensure you can still build https://github.com/eosnetworkfoundation/mandel-contracts (with tests enabled) using the antelope-3.1 branch of Leap and the antelope-3.0 branch of CDT. It shouldn't be necessary to change mandel-contracts code to get it to work.

It is acceptable to still have referenced to EOSIO in both Leap and CDT (even for package names and CMake files) even after this issue and AntelopeIO/leap#1 are completed.

[CongPham05]

great