Improving Environment episodes

Hi,

I would like to work on Episodes 04-conda and 04-virtualenv regarding the use of environments. This includes tackling #18 and #19.

I would suggest either:
* swapping the order of the episodes; or
* merging them together.

Episode 04-virtualenv starts an explanation of why environments matter, but there is 04-conda before that already mentions them. I would argue in favour of presenting VirtualEnv first and then Conda.

Any thoughts?

Thanks,
Vini

Edit: sorry, I did not realize that both episodes were named as "Episode 04". Given this, a merge would make even more sense.

Compare Episodes 04-conda and 04-virtualenv, and review issues #18 and #19 for the requested environment-related changes. Determine whether reordering or merging best resolves the duplicated Episode 04 naming and overlapping introduction; done means the lesson structure presents the environments coherently.

Written by the indexing model from the issue text.