[WIP] SASS compilation variable conventions update

SASS naming convention updates for baseline variable usage on padding and margins, ui-depth extends, along with other small fixes. 

The intent with this is to not have any user-facing impact, and instead move us closer toward having files that use our newer sass conventions.

Currently Includes:
1. - #fff; --> $white;
2. - #000 ---> $black;
3. - margin/padding properties --> multiples of $baseline when possible
4. - replacing z-index with %ui-depth extends
5. - moving multipliers less than 1 (ex: .5, .75, etc) to have 0 prefix (ex: 0.5, 0.75, etc) 
6. - #f2f2f2 & #f3f3f3 --> $gray-l5;
7. - #f8f8f8; --> $gray-l6;
8. - define second amounts are now all using the timing variables defined for both the LMS and CMS. 
9. - rgba shadows are now all using the shadow variables if they line up to existing options. 
10. - %ui-fake-link extend applied where appropriate
11. - %cont-no-list extend applied where appropriate

Next:
- Will migrate other existing white, black, and gray hex shades over to use our current color variables where possible. 
- FED review. 
- Other suggestions for quick fixes? (Feel free to add on any other commits here as well if that's easiest.) 

Future Cleanup:
- Property ordering removed from this in order to limit potential cases where property ordering cleanup would change styles. 


Primary Reviewer: TBD 
Interested Parties: @talbs, @frrrances, @clrux, @andywaldrop. 
@clrux, great idea. I've done the same at previous organizations. I'm all for adding this in (here or in a future PR).

Two things to note: 

1) when we did it at other places, we made each section have a unique (in Sass/CSS syntax) symbol marker for easier find/replace/skipping to each section. Something like this:

`` // Table of Contents`` 
`` // * +Grid`` 
`` // * +Colors`` 
`` // * +Headings`` 
`` // * +Actions`` 
`` ``
`` // +Grid`` 
`` // ====================`` 
`` `` 
`` // +Colors`` 
`` // ====================`` 
`` `` 
`` // +Headings`` 
`` // ====================`` 
`` `` 
`` // +Actions`` 
`` // ====================`` 

- - -

2) We'd want these comments to be in our Sass but not in our compiled CSS, so Sass-syntax comments (``//``) are best.