`bottleneck` dependency installation

[francescolovat]

When running tests in message_data, test_iamc_replace_units[R11] was failing due to a missing module/dependency bottleneck (not included in message_data dependencies).

Trying to fix that problem and pip installing bottleneck, the following error occurred:

error: Microsoft Visual C++ 14.0 or greater is required. Get it with "Microsoft C++ Build Tools": https://visualstudio.microsoft.com/visual-cpp-build-tools/

I had to go to that website and install that Visual Studio component to be able to install it.

However, after discussing with @khaeru , this last step probably wouldn't have been needed if trying to install it using conda (specifically using conda-forge channel).

Possible conclusion:

We may need to make bottleneck a requirement for the conda (rather than PyPI) package for ixmp or message-ix.

It also may be interesting to have a Windows user to test that installation and making test_iamc_replace_units[R11] to pass.