Improve packages concepts section
Improve "deploying" section of docs
Simplify the word "obviates" into "removes"
Improve the templates concepts section
Improved formatting for what is meteor
Merge branch 'devel' into concepts
Improvements based on Nick's CR
Improvements to the concepts section of the docs

Summary: Some small wording and formatting changes. In particular, some parts were outdated and had to be updated.

Test Plan: Read it.

Reviewers: dgreenspan

CC: nim, matt

Differential Revision: https://phabricator.meteor.com/D844