Idea: Reduce number of commands for setting up a plugin

[kdmccormick]

Currently it takes ~4-5 commands:

tutor plugins install blah
tutor plugins enable blah
tutor config save --set ...
tutor images rebuild openedx
tutor local do init --limit=blah

Could we whittle it down to 2?

tutor plugins install blah --enable --configure ...
tutor local launch --limit-init=blah

Would require three changes to Tutor:

• An --enable flag on tutor plugins install
• A --configure flag on tutor plugins install , just like tutor config save --set ...
• A --limit-init flag on tutor ... launch