Create environment : full feature

[conda-incubator]

Create environment : full feature

[pierrotsmnrd]

PR #79

[pierrotsmnrd]

I've tested the PR, thanks a lot for the great work !
I've noticed some improvements that I think belong in this PR :

• 1. if there are no added channels in the yaml composer, don't show channel:[] in the yaml editor. Simply remove the line. Because channel:[] is not valid YAML for an env description
• 2. I've switched to the yaml editor and removed the channel line. When I switch back to the yaml composer, I get a blank page. It should just show the channel section empty.
• 3. When creating or editing a channel, the requested packages section should be unfolded (even if empty), that's often where the users will go first.
• 4. I had unfolded the requested packages section, switched to the yaml editor, and switched back to the yaml composer. The requested packages was folded again. as for the previous point, keep this section open all the time. Also, if possible, keep it scrolled at the same position it was after having switching back from the yaml editor.
• 5. The notification when the env is being created is very good looking ! Once the user has clicked on create, and before the notification appears, switch the whole view to read-only mode to leave the edition mode and refresh the list of envs and namespaces to let it appear.
• 6. When creating an env, in the requested packages section, hide the installed version column. right now it's showing the selected version (see screenshot below), which it shouldn't. Simply hide the whole column when creating.
• 7. Once I go back to the read-only view, the installed version column doesn't appear. We mentioned hiding this column before and I might have been unclear on when to hide or show it :)
• 8. I've edited the description of an env, not the packages, and clicked edit : it triggered a new build. It should only update the description.
• 9. Add a cancel button to switch back from edit to read-only mode.

Screenshot for point 6 with the installed version appearing and showing selected version number, whereas it should be simply be hidden.

[pierrotsmnrd]

Second PR ready for review : #86