Support code snippets from the BE

[anthmatic]

I had originally planned to fix the extra empty file that was generate in #148 but I realized that a while back we added a codeSnippet property to the hubldoc endpoint. Unfortunately, as you can see here https://github.com/HubSpot/hubspot-cms-vscode/compare/ap/support-codeSnippets?expand=1#diff-1942d5c2aca105453d76b423494f061cfe94a22144fcfe87eb80aedc6b7fb67fR1 a lot of the snippets are incorrect.

The main issue is that snippets like

{% gallery ${1:slides} ${2:loop_slides} ${3:num_seconds} ${4:show_pagination} ${5:sizing} ${6:auto_advance} ${7:transition} ${8:caption_position} ${9:display_mode} ${10:lightboxRows} %}"

are missing the argument syntax, so ${1:slides} should look more like slides="${1:slides}"

I'll work on getting those updated before merging this in.

[jsines]

LGTM

[TanyaScales]

Closing in favor of #243