WIP - Add pretty print mode

[bpringe]

This pull request:

Resolves #327.

Introduces the following change(s):

• Adds pretty print setting and defaults it to true - to pretty print by default
• Makes all evaluations pretty print when pretty print setting is true, else no evaluations are pretty printed
• Adds a toggle in the status bar to easily toggle pretty print
• Removes all pretty print commands in favor of this setting/toggle

I have:

• Read How to Contribute.
• Made sure I am directing this pull request at the dev branch. (Or have specific reasons to target some other branch.)
• Made sure I am changed the default PR base branch, so that it is not master. (Sorry for the nagging.)
• Referenced the issue I am fixing/addressing.
  • If I am fixing the issue, I have used GitHub's fixes/closes syntax
  • If I am fixing just part of the issue, I have just referenced it w/o any of the "fixes” keywords.
• Created the issue I am fixing/addressing, if it was not present.
• Updated the [Unrleased] entry in CHANGELOG.md, linking the issue(s) that the PR is addressing.

Ping: @PEZ, @kstehn

[bpringe]

Still currently a WIP, as the title says. I just wanted to branch off of dev on my fork and reference the issue.

[bpringe]

@PEZ @kstehn This PR is now complete. I tested the vsix (built locally, I couldn't find how to access the one built by Circle CI).

[PEZ]

Awesome This lets the user have to think about pretty printing as much. Thanks for the help with improving Calva!