Update compute environments page to accurately reflect conda and clean up

[troyraen]

Compute Environments page needs to be updated to reflect current conda environments and instructions for working with pip and conda should be cleaned up.

• In the conda subsection of "Environment Types" it says, " in the high-energy container image". This image no longer exists. The referenced environments are now tin the default (and only) image.
• List the current conda envs in the "Pre-installed Environments" section.
• Include instructions about how to view installed packets from the command line (eg, pip freeze). Maybe put this in the "Pre-installed Environments" section and also move the "Inside the Console" instructions from /intro-forsc#view-preinstalled-software to this section? That intro-forsc page is geared towards people who don't have an account yet so maybe leaving "Outside the Console" instructions there but moving "Inside the Console" would be a better split.
• The activation instructions for pip envs appear three times but conda instructions only appear once. Related info about kernels is also repeated three times. Consolidate. The paragraphs under "Working with Python Environments" should probably be moved/removed and replaced with a much shorter intro to that section. Activation instructions and kernel info should probably appear under "Select an Environment" only.
• Rename "Select an Environment" -> "Activate an Environment"?
• Many sections need both pip and conda info. Use definition lists so it's easy to find the desired info.
• Add conda info to "Update an Existing Environment".