Packup UI update

[samontea]

Making the packup buffer interactive to allow for the user to more easily select a subset of the packages that they wish to update.

It would also help us prepare for the work necessary to complete #56. This can be considered party of that issue.

Acceptance Criteria:

• Must allow for user to select packages to update w/i a read only buffer
• Must provide help instructing users how to interact w/ the read only buffer

[cg505]

dis gon be sick

[cg505]

@samontea Close this issue?

Leaving a couple notes for future reference: support n and p like magit/dired. recursive dependency resolution?