Resolve "Windows Conda package"

Closes #723 (closed)

Notes for future self:

• CI jobs for windows are run on the machine vp-bcu-ci
  • you can connect to it via remote desktop with your login (thanks Samuel for giving me permission)
• Conda envs are persisted (no docker) so you can connect later on to see what packages are installed, do tests.
  • pay attention to previously existing channels (like stable)
  • also some windows packages may not have the same version on esrf-bcu and stable (like silx)
• You don't need to install all bliss requirements in buildenv
  • only conda-build is required (and maybe python=3.7)
  • pay attention to the version of lz4-c (cf error below)

File "C:\Miniconda3\envs\buildenv5\lib\site-packages\libarchive\ffi.py", line 57, in <module>
    raise ImportError("Failed to load libarchive library from %s - are any dependencies missing?"
ImportError: Failed to load libarchive library from %s - are any dependencies missing?Is your environment activated?

• In case you get this error during conda build:
  • this problem is caused by a DLL naming issue
  • conda-build expect lz4-c>=1.8.3 from conda-forge, whereas higher priority channel esrf-bcu comes with lz4-c=1.8.2
  • so make sure you install the good version or you can use this (ugly) trick:
    • copy C:\Miniconda3\envs\buildenv\Library\bin\lz4.dll C:\Miniconda3\envs\buildenv\Library\bin\liblz4.dll